Region Free between non-Japanese systems, JP titles Region Free with circumvention utilities on non-JP systems.
This one is quite short and sweet – with the exception of a couple of PAL carts having timing issues on American Master Systems, PAL & USA carts can be freely interchanged between their respective regioned consoles.
Unfortunately, due to having a completely different physical shape, Japanese Mark III carts require an adaptor before they are able to run on Euro/USA Master System consoles.