Unlike regular flip flops these actually provide some support for your feet, and don't require the constant "toe grip" of other thong sandals.  I learned the hard way my first year of teaching on a slab floor that a couple of months standing in flip flops could result in months and months of pain and the inability to wear flip flops for longer than a rare excursion to the beach or pool.  These, on the other hand, provide support at the arch and have enough of a molded foot bed that the shoe is held on to the foot and doesn't require your feet to do anything to hold them on. I've bought two pair of the Skechers brand, and I have to save I am quite comfortable in both of them.

This pair, I wore all during vacation on the Texas coast at a hotel with slow elevators, so I chose to take the four flights of stairs most of the time.  Since I walk two to three miles daily for exercise, (not in this type of shoe), and have for over ten years, I certainly didn't expect any kind of work out from a pair of shoes, but I did have noticable muscle soreness in my calves after about two days of walking in these.  Now, the calf is not the area that I am most concerned about, but at least it indicated to me that it was working a muscle group harder than it would have been otherwise. There is just no real good way to judge if these will help you "tone up", but I figure if it burns an extra few calories a day and works out an extra muscle or two, that's a bonus!

One note on sizing:  I originally purchased the Champion version of FitFlops/Tone-Ups at the big box discount shoe store and they were huge!  I wear a 9 to 9.5 and I got a 9 in the Champion and could easily have gotten an 8.5 or maybe even 8 if they were long enough. I do have to do a little bit of a toe-grip with them, but they seem to have identical soles to the Skechers. Both pairs of Skechers Tone-Ups I ordered in a 9, but wish I had ordered a 9.5.  So, maybe you need to try these on in a store first?  I got these at Academy for 39.99.