Your first point is really up for quite a lot of debate. Whilst they're seen by many as 3 of the best schools - I've seen lots of people debate this claim in terms of the calibre of pilot they output. That being said - just looking at which airlines endorse them compared to other, cheaper, schools - you have to consider whether it's worth it. I can't give a definitive answer on this, but I would guess that if they had 2 applicants who were exactly the same other than the fact one went to one of the three and one went to another school, then the FTE/CTC/OAA student would get it.
Of those 3. FTE generally appears to be the best value for money. Especially on their MPL schemes. (Only) £90k (I think the ATPL is €115,000. But that includes accommodation, full board, training materials and internet for the entire duration of the course. The same can't be said for CTC. I'd encourage you to look deeply into all three schools, what's included in the price and what isn't.
As for assessments. I think they're good fun. If you're good with video games/have any flying experience - aptitude tests wise you should be fine. You can purchase and download some PILAPT practice things online for not too much money. Latestpilotjobs I think was the website I used the first time. The maths and physics tests generally are GCSE level with some AS, nothing too difficult.
I've been trying Cadet schemes (unsuccessfully) for a year now. Any more questions I'm happy to have a go at answering them.