The USB hub looks like a much better device than mine - notably, it does USB 3.0
That helps cover the problem of overcurrent but it won't do anything to prevent a gigantic ground current travelling through the USB cable into the PC chassis and out the power cord to ground. That's why a lot of people run their PC on battery - it removes the ground path.
I haven't done that. Maybe I should but, frankly, I have never used my AD on anything over a few volts. It just hasn't come up! My main power supply has current limiting (and the AD has severe current limiting, especially when powered only through the USB port) so I don't expect to see a lot of current coming down the ground wire.
Do you expect to do a lot of mains work or perhaps mess around with switching mode power supplies? I wouldn't do that with an AD even though it is definitely workable. You just need to watch Dave's video on how not to destroy a scope.
Pay attention to this: When you run the AD with flyleads, the scope channels are floating. You need to hook up both leads for each channel although you may often ground the striped wire (you'll see what I'm talking about), or you can take a differential measurement across a resistor, for example. Nevertheless, there is no ground reference even though one of the black wires probably needs to be connect to the DUT ground. RTFM re: ground reference.
However: When you use the BNC adapter, the shell of all 4 BNC connectors ARE connected to ground - just like the ground lead on a real scope or the BNC on a signal generator. All of a sudden, you have lost the differential signaling capability that was provided by the fly leads. The fly leads had a common mode limit (voltage above ground) but the inputs were truly differential.
I encourage you to read everything you can at the Digilent site. Maybe watch the videos... The AD is a fantastic tool but it's usage may not be self-evident.
But truly differential inputs, how cool is that? Sometimes you want to measure the voltage drop across a component that isn't grounded. Yes, you will have to remove the BNC adapter and use the flyleads but, when you really need to do this, the AD is a nice way to get it done.