So I finally dismantled one, and here's what I found. First, there are three screws: two small Philips head screws behind the display cover (as per redsonic's pics back on page 1 of this thread), and a tiny Torx head screw under the "QC" sticker beside the USB hole:
Opening it up:
Here we see the motor and cam. A little trick is that on the right of the PCB you can see a small switch - this is engaged by the latch when it opens to tell the microcontroller when it's open and can stop, wait a tick, and reverse to release (close) the latch. With the device dismantled like this, the motor and cam just goes around and around for a short time, sometimes even stopping with the cam holding the latch open, whereas when you watch the latch with the lock assembled, it clearly goes one way, pauses, then reverses - you can hear two distinct movements.
The lock body is all cast metal, as I kind of expected from the heft of the thing (but wasn't clear from redsonic's pics), while the front cover (with the PCB mounted to it, the buttons and display) is made from plastic. Everything that's in contact with the shackle is made of some kind of metal, not plastic. I don't think it will stand up to too much violence though.
While I had it open, I also shorted the reset pad with a bit of wire through the hole in the front cover (under the display cover). When I did that, the whole thing just died, as if the battery had run down. To get it to respond again, I needed to plug the USB power supply in, at which point it came back to life, fully reset (and with the H+M "emergency reset" feature re-enabled). That behaviour suggests the "reset" simply shorts the power, causing the battery protection/charge circuit to isolate the battery until it's put back on charge. If it was an actual microcontroller reset, I'd have expected it to restart immediately.
I've now epoxied the display covers back on (with extra glue in the screw and reset holes), and disabled the emergency reset. Emergency releases from now will require a great deal more violence (or a shim, if I've omitted the shim-guard)...