The "other hardwire kit" for A810 (and all 70mai cam using type C power input) is UP03 - a simple and small power converter (~5cm long).
4G hardwire kit UP04 is a replacement for UP03, with 4G connectivity. The size is ~6cm diameter x 1.5cm thickness. UP04 is compatible with Omni when it's released, and with later cams as A810, A510. Standby power consumption is 15 mA (because of 4G always on connectivity). Cut off voltage is configurable at 11.8V or 12V or 12.2V. You'll get a notification via phone app when it's going off to protect battery.
The 4G kit adds remote monitoring and alert. The cam can be left off (parking mode off), but remotely the cam can be wake up via 4G kit to show video surrounding the car, or to be put into parking mode. If the parking mode is left unactivated at remote connection, the cam will be back to power off mode after 5 min.
There are 3 variants of UP04 with different mobile frequency bands - Chinese local, International, and North American. However the NA version is not available yet.
Hope this clarifies.