I had a couple more minutes tonight, so I was able to break one open and briefly look at its guts.
The Black Arrow eWallet has an STM32F205RGT6 rather than the STM32F205RET6 that the Trezor and the BWallet have. This means that the eWallet has twice the flash storage on the chip. 1MB vs 512k.
Clearly, Black Arrow has filled that extra space with nefarious HCF opcodes.
Also, the pcb is super thin, and the OLED's ribbon cable is folded pretty sharply when in the case. There are some test pads scattered around on the board, but no clear debugging header.
That's all for tonight. I'll try loading some Trezor firmwares on it soon.
I have yet to see Black Arrow post source code, or even firmware binaries. So if I attempt writing a Trezor firmware on it, I'll have no way to get back to its factory state.