They're really the 1st minimal sandals cheap enough for any kind of mass adoption.  Everything previous was ridiculous or too minimal to justify the price.  The 1st surprise was how heavy they were.  They're at least as heavy as the Asics Hyperspeeds & definitely heavier than optimized racing flats, so probably more suitable for a long trail run than going fast.  

Sole thickness including the tread is 4.6mm.  Without the tread, it's 3.3mm.

Thickness increases to a solid 4.8mm for the strap lugs, so they made some effort to keep them from breaking off.

The heel strap is common nylon with just a smidge of silicone.  The lace has a hair of elasticity to it, but isn't bungy cord.

Contract manufactured in China, so if there's any reason Chinese investors are driving houses to 8 figures, blame their $40 sandals.

The upper pattern.

The toe plug seems to be string cast in a plastic mold.

Heavily rounded, to keep the toe flap from catching & to keep your heel from sliding back during ascents.

The 1st run was a 10 mile disaster.  The right paw never did fit right, while the left paw managed to fit.  Got blisters from both toe plugs & blisters under both paws, very symmetrically.  They managed to hit 10mph.  The problem is the toe plugs are sideways, which makes it equivalent to 5/16" of material going through.  The paw facing rubber is very aggressive on your paws.  They're trying a bit too hard to keep your feet from sliding around.