I did a PPL and paid up front. It saved me about 500 quid so was worthwhile.
I presume you DO like flying as what sort of Plonker would throw away £5k on something they have never tried, bit like buying a car without having test driven it....?!
Go on to the Companies House website. Order the last set of company accounts (costs about £5-£15??). Even if they're abbreviated, better than nothing. Do a few liquidity ratios and come to your own conclusion. Other than that, other indicators of its ability to continue as a going concern would be how long it’s been around and the amount of aircraft it operates.
Good luck