I have several pairs of Chacos with the yampa sole and was very happy. The unaweeps were on sale so I tried them. They are lighter with an articulated sole giving more traction and a softer ride. The sole is still Vibram, and I think it will outlast the yampa sole. Chacos are the best sandals, but you must get and wear the correct size. I have a high arch (supinate). My shoe size has gone from US9.5 to US10.5 over the years (not because my feet are bigger). Chacos still use the sizing of my youth. I first got 11, fearing 10 would be too small. The 11 was too big but it provided protection for stubbing my toes so I wore it for 2 months--until a sharp pain occurred in one toe. I downsized to 10 and tried again. The size seemed at first just right, but the straps still hit the forefoot at the wrong place. I went down to 9. It looks too short (sort of like a Japanese woman on getas) but they are almost perfect (US9.5 would be perfect). Almost 2 years wearing nothing but Chacos and walking not less than 1 hour each day. I have even solved the rainy weather problem (I pull NeoSport neoprene diving socks over my regular socks). I plan never to wear shoes/boots again. It is also essential not to tighten the straps too much. 2 fingers should easily go under the straps. Once you adjust them properly, they do not need to be adjusted again (ever).