One pair is relatively thin, just two 6mm layers of rubber soling sheet glued together. There are little leather tabs on the side and a loop for between the toe sandwiched between the layers of soling sheet. The leather lace goes through the tabs and the loop instead of going through the bottom of the sole. They are very minimal. I have worn them on walks at the university where I work and I brought them on a camping trip and just wore them around camp.
I added a suede top to these and 10mm black leather laces.
I wore them on a hike last weekend. We hiked up Rattlesnake trail to the Connector to the waterfall on Tunnel Trail, then down Tunnel to Mission Ridge and back down to Rattlesnake. I struggled a bit on the Mission Ridge trail, especially on the downhill part. I usually struggle and there's always a section or two where I have to scoot on my butt. It was no different this time, but with the sandals on, I felt like I had to blame the sandals. Other than the butt-scooting, I was pretty slow going down the hill. I didn't feel confident I wouldn't slip and fall, and the thong between my toes hurt a little.
Still, I was pretty happy I was able to make a pair of sport sandals and hike on a really gnarly trail in them. I had no trouble on the regular trails. Rattlesnake was fine. Tunnel was fine. Going up hill or on rocky sections or down a normally-graded trail was not a problem at all. My feet were bare with no socks on. I can't even do that in my Chacos.
I'm thinking maybe another try. Go with the same system with the loops and tabs sandwiched between two layers. But for the bottom layer, use a lugged sole for bullet-proof downhill traction. I haven't decided what to use for the top layer. The rubber is nice because it will dry fast if I go through a creek. But it's rough on my skin. The vegetable-tanned leather is nice because eventually it molds a little to your feet and it is flexible yet very protective against rocks. The suede just feels nice. I haven't decided what to do yet.