Tried these groups for the first time this holiday season.
USA lost an item of mine saying they never got it. I did a UPS claim and then the retailer sent a replacement to my home address. Had some close calls with MYS but they all came through. Buyformeretail was the best of them by far. Fast pay and service. But yeah USA and MYS seem like there's some risk working with them.
Being subscribed to these groups often on email they'll tell you when there's a drop on a hot item. Needless to say I made more when I was able to grab xboxes and sell on my own vs. send to them. Same for coin deals. But all of these groups made plenty of money from my buys as well.
Stacking Amex deals or cash back links for the items with commission worked out as an easy bit of money and SUBs with a few clicks.