Mark,
I haven't heard that particular compilation, but my experience with the label is that the transfers are solid. For example, their reissues of Graham Collier's music were excellent. And I've heard positive things about their reissues of Arthur Blythe's Columbia recordings.
As to the legitimacy, I can't say. I assume that in some cases BGO is reissuing material that's fallen out of copyright (in the EU/UK) and in other cases obtaining permissions from the artists/estates. I seem to recall that the Collier reissues were legit. But don't quote me on that.
Sorry not to have something more definitive.