score:2
The third-party "ETA Australia Online" site you link, if read carefully, notes that only citizens of certain European countries may use its service; other nationalities which are eligible for ETA are not allowed to use the site.
This is a bit of speculation, but I suspect that this is because they do not apply for an ETA on their customers' behalf but rather for an eVisitor Class 651 visa, which is available only to citizens of the same European countries as listed on the third-party "ETA Australia Online".
However, the eVisitor stream is available to citizens of eligible countries for free from the official IMMI website, so the "discounted" price from the third party is not such a good deal.