Most software is written to work on PCs and simply "ported" to Macs; the bits that don't work entirely properly or naturally most vendors don't seem to worry about, and Mac testing is less than rigorous (as if any products are well-tested before release any more). So while products may be "Mac-compatible", they aren't really designed to work on Macs, more's the pity. When you go Mac, you only go back kicking and screaming.

Thus "rewriting to work on Macs" may simply mean that the innards were redesigned to be more fully cross-platform and better integrated with Mac interfaces. It may also have been a euphemistic way of saying "we fixed the registration change which Apple foist upon us without sufficient notice."

Given my experience with PrintMusic, I'm inclined to support your decision: if their mid-range offering--and probably their top-end offering as well--can't even print simple tunes as normally notated, they've seriously missed the boat. As a basic guideline, there shouldn't be anything you can do in Barfly that you can't also do in PrintMusic, regardless of the many things PrintMusic can do that Barfly can't. But I have no experience with Sibelius, and won't shell out $500 for a product I can't get detailed information on prior to purchase--I've been burned too many times. MakeMusic at least lets you download the complete user guides for their products.

So first I'd advise going to Sibelius music repositories, downloading their free reader and sampling scores of similar music to ensure they have ALL the features you need. Of course, this will only tell you definitively about their top-end offering, but if I recall, they don't have a mid-range product or I'd have transitioned when I ran into the Finale registration fiasco. (Anyway, "mid-range" these days tends to mean "bait and switch", with key features even the basic user needs unsupported.) It also won't tell you how easy or difficult the program is to use. Wonder if Consumer Reports has ever done comparison studies...