Did one, had a brilliant instructor, passed on Saturday morning. Hard work - it is amazing how knackering reversing around corners in Hangleton can leave you every evening - but worth it.
I did one of these many years ago and passed first time. If you can afford the time off work, it's much better than having to drag it out over several months.
I did one, it didn't do me any good, but I think that was partly because it snowed the first day I was supposed to start so I actually only ended up with 2 days of lessons and then the test.