Yes, it can be tough. The initial tear away from an existing job, especially if you've been there for a while and enjoy it. The move down to Bournemouth, leaving the wife & kids at home, going mad at your own company in a cheap hotel or rented room for 6 months (or a lot more!). The feeling of fear (and the smell) everytime summatives come around - even if they're not for your course! Oral boards, just to give you an extra roasting if the writtens and the summatives aren't enough. BUT, once that's behind you, nothing can describe the feeling of receiving your "yellow book", knowing you've beaten the odds, and that you survived the initial part of your training.
It doesn't stop there though, I'm now in my 22nd month away from home - 12 months in Bournemouth, and now 10 months at a unit, and the wife / kids still haven't managed to join me. But the highs keep coming - the further through the training you progress, the more you get to do, until eventually the "man from the ministry" is summoned to see if you're up to the job. Fortunately, I was, and am now in my 2nd month of being a valid controller, and enjoying it tremendously. The stress has subsided a little for now, as has the bookwork (until I really start progressing with my approach training, anyway), and I can relax a little and do the job, instead of train for it.
Yes, the pass rate seems to have dropped at the college at the moment, for whatever reason, but in the past 10 months NATS have also adjusted the course to try to improve matters. Yes, there is quite a backlog for training reviews. However, the failure rate hasn't reached 100%, so some people are still passing, and if you don't try it, you'll never know. You have to take the decision very seriously, but if you're prepared to put in the work, accept the grief when someone on your course fails, or worse, gets chopped, get over any setbacks you suffer yourself, put up with being a NATS pawn for 6 - 12 months, and possibly beyond, then I, and I am sure a lot of others on here, would wholeheartedly recommend you go for it.
I guess I painted a bleak picture there, but you've also got to remember that Bournemouth's a great place over the summer - there's no shortage of pubs, clubs and bars to visit (and discuss the course work, naturally!), take your MATS 1 down to the beach and enjoy a beer or two, the instructors and other students are always willing to help, and once you're at the unit, my experience has been fantastic, with the ATCOs that will be your mentors, and then your colleagues eager to help everyway they can.
Go for it, work hard, play hard, and enjoy it!