There's no way I'd wear sandals made from old tires. I used to work at a recycling place which ground up old tires. The wires in the steel belts and beads are bad news for feet and if they're damaged in any way (like being cut into a sandal pattern) they'll eventually work their way out...possibly into ones feet.

Ever since I helped a guy who had a tire bead wire go through his rubber boot, then his foot, then the boot again to the hospital I've been super careful with cut up/damaged/shredded tires.