I ordered three (classic red, navy and navy/green striped) of the "2 piece classic" Nato bands from Clockwork Synergy and got the delivery today. The bands are a little thinner and more flexible than the Apple nylon bands, and are constructed completely differently. These bands have the standard "lugs" for attaching to the Watch, as opposed to Apple's molded connectors. Additionally, these bands have two metal loops for the end of the strap that are sewn in place, where the Apple nylon bands have a single "floating" loop made of matching nylon material.
After having worn one of the bands for most of the afternoon, I can say it is quite comfortable - and a bit more casual looking than the Apple nylon bands. When I first put it on, I noticed a slight scratchy feel to the inside (side of the band that actually touches my skin)... so if you in any way have "sensitive" skin, it MIGHT be a bit of an issue. The bands are also slightly shorter than the Apple nylon bands.
For the price ($24.95 with a 20% discount via coupon code), I'd say they are keepers - but I will wear them in much more casual environments.