I've been climbing in the 5.10 Mocs for a few year now and they are great. I wear a size 9.5 street shoe (as measured on one of those foot measuring devices with socks off), and I wear the Mocs in a size 8.5. These were very tight originally but have stretched and are now perfect (comfy while climbing, but not what you want to stand around in too long). Very sensitive and sticky, great for edging, smearing, and crack climbing. I love the slipper design, nice to be able to just pull of and on when you need to with no lacing. They have held up well through many days of gym and outdoor granite sport climbing and bouldering. I know there are many great shoes out there these days at great prices, but if sized right and given a good break in, this one will not dissapoint!