When I first put these on they feel extremely comfortable and supportive for the first couple of hours. If I don't do a lot of fast walking, they are comfortable for longer than that. The part that is uncomfortable during brisk walking for me, is the strap between the toes, and the little hump that is supposed to be like a toe grip. There is just too much contact and rubbing on those parts.
When I just wear them around the house, or for light walking/shopping, they are very comfortable though! I got my first pair last year and by the end of the summer, even the more vigorous walking was more doable. I'm hoping that's is the case again this summer because I love the look and feel of these thongs for the most part.
(Also, they are great for watering my yard and flowers, the water drain holes work like a charm!)