[fennecfoxen]

Some bike racks are designed to maximize capacity, and you're supposed to roll your front wheel into the rack, between some very narrow vertical bars. You could probably cut the bars with any decent bolt cutter, and certainly with a hacksaw. The U shapes and up-and-down S shapes, where you can move your bike alongside a thick element and lock the frame, are fundamentally better but will still be cuttable.

[buran77]

I've seen thieves cut street signs and sturdy bike racks to take a bike. I don't really see this material working for relatively thin bars like a regular U-lock. The base material is aluminum which is relatively soft. Thieves would just switch to shearing action tools to cut through it and if the bar isn't very thick they'd probably only encounter 1 or 2 of the ceramic beads and push them away through the soft metal. They might even use a portable torch to soften it up before cutting.

Conceivably you could have a thick Proteus core with a thick hardened steel casing but it makes the lock either unwieldy or terribly expensive. Maybe they will be able to embed the ceramic beads directly in hardened steel, making it lighter and more resistant to cutting.