Remember that the topic is E (or Eb) minor. Some of you are clouding the issue by thinking in terms of E/Eb major.

E minor is the relative minor to G major; it's not an uncommon key at all, nor particularly difficult to play in. Note that all open strings fall on notes in the natural E minor scale.

Eb minor (6 flats!) is highly unlikely for your situation. It's not a typical key for any common folk instrument--and certainly not an easy key for concertinas or melodeons of any flavor.

I believe Lucius was trying to make this point elliptically with his "Judentanz" reference. "Der Juden Tanz" (The Jewish Dance) was written in the 16th century by Hans Neusidler (not Jacob Newsleider). Its melody is in C# (Myxolydian?) while the harmony is in D--think Darius Milhaud anticipated by a few centuries.

In other words, if you were to accompany concertinas and melodeons in Eb minor, the effect would be jarring, since you clearly wouldn't be playing in the same key as the rest.

[Note that for an Eb wind instrument, Eb minor would require a fingering with 3 flats. A Bb instrument would require 4. E minor would be fingered with 3 or 4 sharps. Neither would be a typical selection for a wind-based group, so we can dispense with that red herring.]