Metta towards yourself - useless?

On the contrary, how can you ever send good wishes to other person if you don't have same wishes for yourself. This is sheer hypocrisy. It sound like some kind of Buddhist impersonalization and nihilism.

JUst do real metta with concentration and determination and these kind of statements won't bother you.

SN 3.8

Then the king went down from the palace and visited the Blessed One [and told him the whole story.] And the Blessed One, understanding, thereupon uttered this verse:

Though in thought we range throughout the world,
We'll nowhere find a thing more dear than self.
So, since others hold the self so dear,
He who loves himself should injure none.

I guess that what "(useless, but a good example)" might have meant is that in general people already feel metta towards themselves (even if they don't always know what's good for them):

It is because they already feel metta towards themselves, that is why the Visuddhimagga recommends it as a first stage -- e.g. to remember what metta feels like, before transferring that to other people who are less easy -- that's what calling it "a good example" might have meant.

It's not saying "metta is useless", but I think it is saying that "cultivating metta towards yourself" is preliminary and not the purpose of the exercise.

Are there any specific sources for this statement, or is this based on a determine school?

The advice to start with oneself as a subject comes fro the Visuddhimagga -- which asks rhetorically whether the practice is justified by the scripture (as if self-regard might seem like a questionable practice), and which references the sutta I quoted above as its justification for the practice.

I've also seen this quote ...

These four attitudes are said to be excellent or sublime because they are the right or ideal way of conduct towards living beings (sattesu samma patipatti). They provide, in fact, the answer to all situations arising from social contact. They are the great removers of tension, the great peace-makers in social conflict, and the great healers of wounds suffered in the struggle of existence. They level social barriers, build harmonious communities, awaken slumbering magnanimity long forgotten, revive joy and hope long abandoned, and promote human brotherhood against the forces of egotism.

... which might imply that "metta" is intended primarily toward "living beings" (i.e. not only "oneself"), and also in "social situations", and perhaps specifically the opposite of "egotism".

Householder Louis, interested,

as one stated in an answer, such a statement comes often from those actually having Nihilist Views. This monk, by such a statement, not only disregard the elders, but also the Buddha and his teachings.

Next to the fact that all traditional followers start practicing metta with having such for themselfs, a matter of right view, even the Karaṇīya Metta-Sutta starts with metta, goodwill toward oneself.

Karaṇīyam'atthakusalena, yaŋ taŋ santaŋ padaŋ abhisamecca:

He who is skillful in his welfare, and wishes to attain that state of Peace should act thus:...

So the drive is actually metta toward oneself. One doesn't have goodwill toward himself is never able to practice toward and on the path.

It's good not to stick much to "western/modern" ideas, since for the most they come from a Nihilist background, (previously) follower of other sects.

Note that many are disciples of this modern sect leaders here and reflect similar Nihilist and Jain-Uposatha approaches.

For mor an the topic see previous answer on: How to view people with metta and karuna?

Also Buddhadasa is one of this modern Sect leader, with same approaches like the young Canadian monk:

Does this statement by Buddhadasa Bhikkhu conflict with traditional mettā meditation?

Sakko ujū ca sūjū ca (being honest, very honest: a very prerequisite, not only for metta practice with conductive effects)

The Buddhas words on one occation: "Do you really love yourself? Are you going to content yourself simply with the food, clothing, shelter, and medicine of lay life even though this means staying in the cycle of birth, aging, illness, and death? Or would you really like to put an end to suffering?" (See: "Selves & Not-self", by Ven. Thanissaro on more about general instances on the roots here)

Metta toward what is dear and near, starting by really having goodwill toward one self, is right effort, is the foundation, when added samvega, for the path and the only way not developing something harmful for oneself and others, even when the four noble truth are not developed. Other kinds of metta will be hypocritical, void of virtue, void of path toward Brahma-Vihara, access and path. Even King and Queen realiced that by themselves:

...“That's the way it is, great king! That's the way it is! Those who engage in bodily misconduct, verbal misconduct, & mental misconduct are not dear to themselves. Even though they may say, 'We are dear to ourselves,' still they aren't dear to themselves. Why is that? Of their own accord, they act toward themselves as an enemy would act toward an enemy; thus they aren't dear to themselves. But those who engage in good bodily conduct, good verbal conduct, & good mental conduct are dear to themselves. Even though they may say, 'We aren't dear to ourselves,' still they are dear to themselves. Why is that? Of their own accord, they act toward themselves as a dear one would act toward a dear one; thus they are dear to themselves.”

That is what the Blessed One said. Having said that, the One Well-Gone, the Teacher, said further:

If you hold yourself dear then don't fetter yourself with evil, for happiness isn't easily gained by one who commits a wrong-doing.

When seized by the End-maker as you abandon the human state, what's truly your own? What do you take along when you go? What follows behind you like a shadow that never leaves?

Both the merit & evil that you as a mortal perform here: that's what's truly your own, what you take along when you go; that's what follows behind you like a shadow that never leaves.

So do what is admirable, as an accumulation for the future life. Deeds of merit are the support for beings when they arise in the other world.

Piya Sutta

One rejecting that he is worthy to have goodwill with himselves, would not fear to harm himself and break his virtue. Those who act like fools often say "I accept hell for the well-fare of (some) other" or act "Jesus-like" and in foolish hero-ways.

Searching all directions with your awareness, you find no one dearer than yourself. In the same way, others are thickly dear to themselves. So you shouldn't hurt others if you love yourself.

Rājan Sutta

The Buddha himself started his journey being dear to himself and all real warriors would follow in this way. A nice ballad has been written by one of them, reflecting the way "ex-bodhisattas" start to walk the path:

The Ballad of Liberation from the Khandhas

...Once there was a man who loved himself and feared distress. He wanted happiness beyond the reach of danger, so he wandered endlessly. Wherever people said that happiness was found, he longed to go, but wandering took a long, long time. He was the sort of man who loved himself and really dreaded death. He truly wanted release from aging & mortality. Then one day he came to know the truth, abandoning the cause of suffering & compounded things. He found a cave of wonders, of endless happiness, i.e., the body.

An at least, every developing of metta, Brahma-Viharas, in the good old tradition of the noble ones starts with oneself:

Ahaṃ sukhito homi May I be happy.

Niddukkho homi May I be free from stress & pain.

Avero homi May I be free from animosity.

Abyāpajjho homi May I be free from oppression.

Anīgho homi May I be free from trouble.

Sukhī attānaṃ pariharāmi May I look after myself with ease.

(METTĀ — GOOD WILL) Sabbe sattā sukhitā hontu. May all living beings be happy...

As long as one does not understand that what ever, good or bad, one does for oneself and beyond, no developing of right view and path can be expected. It's because beings do either not hold them dear or don't know the way to long lasting happiness, harming themselves in many, even perverse ways, that they being do not even master the way toward the Brahmas, or any Jhana, path or fruit.

What does no like to give and share not even made his at first place?

(Note that this gift of Dhamma is not dedicated for trade, exchange, stacks or entertainment but as a means to make merits toward release from this wheel)