I received the black side-zips yesterday. First thought - my pair definitely look more grey than black. There's a lot of the white 'mould' coating on them. I'll be interested to see how that wears away.
After a couple of hours wear, creases are starting to form where the toebox starts. Not aesthetically pleasing creases, either. My mainline side-zips took a little longer to start creasing up, and the creases form fairly nice 'wear marks'. I would guess that this is because the H&M boots use thinner leather.
As for the sizing, they are slightly more snug than the mainline boots, but I have them both in 43 with no problems.
Final thought? Worth it if you an get them at the very lowest price, and use them for spare shoes that you don't mind getting a bit beaten up. If you want a pair of proper every day side-zips, save up for the real thing.