That's because there isn't much science behind them! Just people trying to cash in on the fact that everyone wants a quick fix to toning and strengthening their legs in my opinion. Not that I'm against quick fixes, just wish they worked lol
I've got fitflop and I walked about 20 miles in them over the coarse of a week while on holiday. Didn't notice any difference. They really hurt my right foot, all along the top and part way up my leg too.
Odd.
However, the Rebok and Sketchers look like they might be better. Pity they are so ugly.
I've got some skechers tone-ups which are a sort of super-flip-flop, and am giving them a go for general use for the next few weeks, lets see what happens!
I'm going to stick with my ordinary trainers for dogwalking for the time being though as my tone-ups are toe-post style and I reckon they will probably rub if I try to do a fair distance (the dog and I generally do a couple of miles at a time) in them.