They're pretty much the lowest price (from the reputable for the 375, and the
lowest among everyone for the 550) on the net, but they both ship for free which
makes it pretty much lower than everyone else because these things are heavy.
So instead of paying an arm and a leg for the shipping of your UPS, you can
get it shipped for FREE here. the 550VA unit has a 28 minute back up time while
the 375 gives you 15 minutes to shut everything down.