Now, from what I've read on this forum, you just shouldn't buy hours in bulk and rather pay as you fly.
I think being aware of the situation is good but ultimately it's your money. Can you afford to write it off? If you are confident about the organisation and are using a credit card which affords some protection then I don't see the problem.
Most people that lose money seem to be fairly clueless about what they're doing, either paying by cash or cheque, and they never even think about the possibility of losing all their money.
There are plenty of places however that I wouldn't even contemplate paying upfront! It's your choice...