I bought a 3-meter long USB C cable from them for data and display transfer, which turned out to be the only USB C cable of that length capable of driving my display at its full resolution and framerate. However, after a year of use, it stopped transferring any sort of data. So while they're probably up to spec, the quality isn't necessarily what their pricing may suggest.

Support allowed me to send it back for replacement as a "one-time exception", though I was well within the common 2-year warranty period in the EU.

We had good results testing Cable Matters stuff here at work, but that was for non-critical use so I didn't go too hard on the tests. (Actually, I didn't go too hard on any of it since it was mostly make-work from a manager trying to cause trouble, but still....)

I was quite impressed by GlobTek (available at Digi-Key) and have been buying those when I need something nice. Their USB-C line are some of the best I've seen, not that I'm a connoisseur.

I've not spec tested them, but astronomy gear is notoriously picky about USB cables and since I switched all of my cables to cable matters a lot of weird behaviors just stopped happening

They are excellent.

Could that possibly be shielding?

I can't say I've seen it on USB-C-esque cables (except maybe a thunderbolt cable a while back?) but I've seen some cables use a type of aluminum or mylar-looking foil between the outer rubber sleeve and the inner sleeves and wires.

My concern is stiffer cables are likely more likely to rip USB ports off the PCB. A lot of devices provide very little support to the USB port which is basically just hanging off pads on the PCB, so a stuff heavy cable could provide a lot more bending force to rip it off.

Phones and macbooks have it done right where the outer portion of the port is built in to the device body, but most other devices don't do this.