A friend of mine has fitflops and says they are excellent but they were forty quid. If imitation ones are as good as imitation Crocs, why not just buy the cheapies first and see how you get on with them?
I bought some trainers with the same sort of sole... have noriced a difference and if I wear them for my usual walk my legs ache more the next day as if I've walked far longer... funny enough its my thighs and bum that have benefited most