Disconnecting the power inserter or pulling the plug on it will turn the preamp on the mast into a giant attenuator, blocking most of the signal trying to get through. Removing the amp and inserter completely is the only way to test reception without the aid (or hindrance) of the amplifier, but I realize that's inconvenient (or worse) in your case. But it's something to consider.
The RCA TVPRAMP1R has separate VHF and UHF inputs, plus an FM trap (switchable), a relatively low noise floor, and gain in the high teens for VHF and low 20's for UHF, I believe. If you use that one, make sure you check the dip switches for proper setting - don't rely on the factory settings, as lately they've been shipped with the switches opposite to what the manual says they are (from what I've read). You want the inputs to be separate, and the FM filter to be on.
It's only a couple of bucks more than the outdoor UVSJ, in fact, at least at Amazon.
http://www.amazon.com/RCA-TVPRAMP1R-...f+preamplifier
Just remember - the amp is only for pushing the signal down long runs of coax and through splitters. The antenna(s) need to collect the signal, strong and clean enough for good reception, on their own, which is why you need high gain/directional antennas where you are, and an amplifier so you don't lose what little they can get on the (presumably long) way down the coax to the receiver(s).