Motorola Solutions and EF Johnson are two different companies. EF Johnson is owned by JVC Kenwood.
When you say "you've heard they are the same" what are you specifically referring to?
Years ago some early production EFJ 5100s used XTS5000 RF boards, but today's EFJ products are 100 percent JVC Kenwood/EFJ.
FWIW, if you are thinking of acquiring one of those early rev 1.1.2 EFJ5100s, unless they are free, pass on them. Lots of problems and they are no longer supported by EFJ.