That said, I am in the middle of collecting the Bloomsbury versions as well (I have 1,2,3 & 5). I had heard that these books vary slightly from the American editions--mostly just swapping out a few British terms unknown to American audiences. But I wanted to read them for myself.
These dark covered editions are marketed as the Harry Potter Adult Set... I don't know how on board I am with them. I guess they are pretty-- I don't think I'll be buying them though.
And I am pretty sure I won't be buying these last ones either, since they won't be made. I actually really like the cover art on these (they remind me of the cover art of another groups of books, but I can remember which ones?!) The link under this picture explains more about these covers and the artist.