Machinegun brass would be less desirable from a reloading standpoint but I don't think any current machineguns are in that caliber. The ad says mixed commercial headstamps. It would be quite expensive shooting commercial ammunition out of an old machinegun.
There are some decent reviews on ammoseek for them. I look there since they can't remove any bad reviews, just respond to them. Seems like they have good customer service if you are not satisfied: