I bought 4 of them a last week from CSC in Calgary, and have had them out to the range already.
These are quite nice mags, really well made. They're crimped, instead of pinned, to limit them to "5 rounds of .50 Beowulf" - which is fine by me, it's a lot harder to accidentally get in trouble with Miramachi that way.
No-tilt follower.
Very clearly marked "5 Round .50 Beowulf" in several places - again, good for avoiding trouble from Miramachi.
If you fill them to the limit with "that other calibre" you can't (at least the 4 I have) quite seat them on a closed bolt. That isn't a huge deal, because:
a) I generally don't seat mags on a close bolt anyway.
b) Even 1 round down, you still end up with a higher capacity than other mags.
Fit and finish is great. I've dumped all 4 of mine a few times already, no cycling issues or problems of any kind so far.