Although I can't find an authoritative source on it the indications do support that assumption that it is USI. Technically USI doesn't have to be bad, it just appears that quality control on the standard is bad (similarly to how USB cables often don't meet the spec and can cause troubles as a result).
Firmware can be checked here: https://gitlab.com/zephray/enchanter
Sure. But USI is bad unless the OEM goes out of their way to make it good, whereas EMR is good unless the OEM goes out of their way to make it bad. EMR is the better tech, and with patents expired, and numerous other benefits such as no batteries needed in the pen, it should be standard now.