Good point about making sure you're ok with the flying school before dropping the big wedge up front.
I did a few lessons on a 'per-hour' charge and got to know the place before putting down the big up-front money. OK, so it means I've paid for a couple extra hours but chances of finishing in 45 are pretty slim anyway from what I understand. If I do, then fine, a couple extra hours paid for afterwards.
Might not work for everybody, but seems to be working for me (he says, touching wood....)