I got the GQ-4X to program some custom 2732s for the Bally -35 MPU. Also used an external 9VDC 300 mA power adapter. About half the time I started the application it would not be able to connect to the burner, so it would go into "demo mode". When it did connect, it would often stop in the middle of burning a chip. This behavior was consistent whether or not I used the power adapter.
I sent the unit back to MCUMall for a replacement, and to my surprise I got a call from one of their techs. He said it works fine and asked if I wanted a refund. I said I'll take it back if you'll walk me through the app and driver installation. When I got it back he helped me install it and it appeared to work fine, no more connection problems, but I was thinking, "This is exactly how I set it up before, why does it work now?"
Sure enough, when I went to use it a couple of months later, it had the flaky connection problem again. I was about to give up and buy something more expensive, but then I tried running it through a powered USB hub. Happy to say it works reliably through the hub, no connection or burning problems. I used a Belkin F4U058TT USB 3.0 hub from Best Buy, but probably any powered hub would work.
My particular unit may have a weak/flaky USB interface, and the tech who tested it at MCUMall may have been using a powered hub, I dunno.