Careful - the M3's percussion is not exactly like the B3's. B3 uses "foldback", which gives you the percussion without dropping the volume of the held tone. M3 doesn't and the volume drops when you engage the percussion.
There are foldback kits that let you fix that though. So you may be able to find a foldback-enhanced M3, or do the work yourself.
Also, the octave-minus-one pedalboard really sucks - plus it's got the little plastic stubbies, rather than the two ocatves of boards on the B-3. And no presets.
Still a VERY good buy. But if I were shopping, I'd go for an L-100 before an M-3. Full octave of pedals, integrated run/start mechanism, a couple of useful presets, foldback perc, built-in reverb...
Daf (former M3 owner, former L-100 user)