I've built on literally hundreds of OOW receivers. One problem they had for a short while was a short ejector. They are all correct now. Make sure you get one with the serial number over 1000 and you will be fine. The manufacturer marks are on the side. Never had any other problems with thier 74 receivers.
I have built on one Arsenal receiver. Nice receiver, but the magwell dimples leave a bit to be desired. Also with the manufacturer info on the bottom, it keeps more realism to the rifle.
I can't wait for Harlen to get his out. I know they will be kick ass!
Mike