I was going to buy some Treks, but after trying them on at a local shop, I prefer the KSOs (and will be buying a second pair). I think the Treks are just a bit too far from the "barefoot" angle the FFs are about - sole not quite as flexible or sensitive and foot higher off the ground (because of the threads). That said, I didn't enjoy hiking on sharp rocks, etc. with the KSOs recently so definitely could see the Treks better for that use (and likely designed for).