For what it;s worth, I have an HP-1 and just bought a 436HP, which I've been told uses the same basic "receiver technology" as the HP-2. In terms of picking up signals, the 436 is much, much better, bringing in things the HP-1 never "hits." Not sure if the HP-2 would perform the same way.
Oh, and as to the USB "charger" thing, I have only gotten AC power to be supplied to the 436 through my laptop's USB port. I have tried four different standard 1amp USB chargers and none of them work--scanner keeps turning off when I turn it off.