That indeed is true nick14, 3% is less than other companies charge. But who told you that this will cover everything? It certainly is NOT in writing (because nothing is). The real question is: if this "approved!?!" scheme goes wrong who is responsible for paying back tax? The consensus appears to be that it will be the pilot, even if the arrangement and the advice turns out to have been incorrect.
If somebody said "fixed charge 3% and you are indemnified against any future tax costs caused by some aspect of the scheme turning out to be unacceptable to the taxman" - then it would possibly be worth looking at. At the moment, as with so many things Ryanair, you have to step into the firing line and hope that your expectations turn out to be correct (and how many will tell you that that such assumptions are unwise?).
And what happens next year when you have signed up and they then announce that it has turned out to be more expensive to run than expected so the charge is going up to 4.5%? You won't be able to do tiddly squat. Nothing ever changes.