Personally I think its a bit unfair to be expecting any flight school to let you down, there are so many that have been around for years and will be for years to come. Do proper checks by all means, just as you would before paying out for any substantial purchase, but as with any business at the moment margins are tight, cash flow tighter and they need all the help they can get. Stapleford seem quite stable and were very helpful to me, they let me pay it in 2 halves, but still gave the full discount for paying in advance. Just put it on a credit card and you should be pretty safe.
I would imagine that choosing a school based on the lowest price could come back to bite you if you hand everything over at once, those that charge more and have been around a while have set those prices so they can remain as stable as possible.
Schools with a handful of aircraft I personally would not feel so confident handing everything over at once, larger schools with many more aircraft of different types have assets that can be released should they really need to do so to survive.