Given that everyone is so agreeing, maybe it's time for a contrary opinion!
I'm learning to fly in the UK, and paid the whole lot upfront to save about 20% (using a credit card).
However, before I did it, I took several lessons with them and made damn sure that:
1. I liked flying (I did!)
2. They were not a total bunch of cowboys (although I'm not sure how I would have been able to tell if they were, at least with respect to the flying)
If that's too much of a risk (and it's all down to your own perception of risk, as with any 'investment'), how about buying a block of time? 10% off of £100 odd per hour makes a hell of a difference once totted up over 45-50 hours and what's the worst that can happen? You lose a grand which you then claim back from the credit card company.
Now about to start my first solo x-country if the weather holds up and have forgotten about the four and a half grand credit card bill (almost!) so it feels like I'm flying for free. Not looking forward to hour 46 though....
Magic!