I'm the aforementioned brother.
I got the KSO model (the Flow is waterproof but too hot for summer walking because of the Neoprene, and the other models have an exposed top). With the appropriate socks, I found them to be very comfortable indeed - like walking barefoot but with some protection. However, because it
is like walking barefoot, I'd not recommend them for walking on course gravel or the like - you'll feel it. They're fine on pavement if you don't need extra cushioning (I was just on my daughter's zoo field trip and spent four hours walking through the zoo with no ill effects). However, they are
amazing when walking on grass/soil/soft surfaces. I hate having my toes touch each other (yeah, I'm a freak), and these are just the ticket.
People
will notice them, though, so that's either a plus or a minus depending on how much of an attention whore you are.