I owned and used both MJ and BK7M. Both are excellent. Midjay has that live Ketron sound. Operating system is really good. Vocal harmonizer was primitive. Vocoder only. Not sure if the plus had the same one.
BK7m has more styles, better lead voices in most cases, lighter weight, smaller. It has far better editing capabilities.
It has no vocal processing, no mic input. Must use external screen for lyrics. No true break/fill (like all Rolands).
Both need external pedals for a lot of operations. Bk needs it more.
I enjoyed both and could easily still be working with either.
BK7 is sure a bargain financially, except you will need vocal processor, harmonizer, external screen, etc to cover all bases.