Yes... basically, the BK-5/3 don't have the audio loops feature, or the user drumkits, and a BUNCH or other stuff.

TBH, the only BK I'd highly recommend is the BK-9. Perhaps if some of the new stuff gets added to the BK-7m or BK-5, they'll be up there, but for now, the BK-9 is the one to go for.