To claim for delayed flights compensation in the EU under (EU rule 261/2004) should only cost the price of a stamp to your airline. You should not pay a 3rd party company to do this for you. There are some very helpful tips that are provided by Martin Lewis (The Money Saving Expert) in the UK which I followed and were successful in my claim. I presume it is the same process throughout the EU?
There are some key points you need to be aware of before you claim though:
The link above also provides more detail and includes some standard letters that you can use for your claim as well as helpful addresses to airlines and the EU regulation body for appeal. You are essentially claiming to your airline under EU rule 261/2004 and they will judge the claim on a claim by claim basis. If rejected you can appeal.
I imagine the companies you found that offer this service for 25 EU are just doing the same thing. They will take a percentage cut of any claim won and charge an admin fee of 25EU a time. My advice, stay away.
Credit:stackoverflow.com‘