You may already know this but not all Tesla chargers are open to non-Teslas and, something I found out recently, not all Tesla chargers are cheap.
As for compatibility, I think all of the long ranges were updateable (and all of the FL). Some of the standard ranges were also updateable but it depended on the part number of the CCU.
About a year ago, either on here or on facebook, someone posted a technical note from MG that gave the part numbers that were compatible but I haven't been able to find that message since.
Edit: I just found this old post
VOTE TESLA SUPERCHARGES with MG5
It still isn't the full details but it might help.