Thigh trimmers, shed excess water temporarily... but is it even helpful at all then?

If you are trying to lose fat from your thighs, then no. Contrary to what many believe, you cannot remove fat from one part of your body and not from others; when you burn energy through exercise, you will siphon off fat from stores distributed around your body. So you would be better off doing exercises designed to burn a lot of calories, rather than ones concentrated on the thighs. In fact, if you make your thighs do all the work, they will get tired more quickly and you will burn fewer calories. However, fast walking is a decent aerobic exercise, so it should help; I’m not certain how aerobic exercise compares with anaerobic exertion like running or intensive sports for weight loss.

Of course, if you are trying to make your thighs firmer and stronger, then you should obviously work them specifically just like any other muscle, using squats, lunges, plyometric jumps, etc.