Expensive vs. cheap UPS for server

Hi, I need to get my server a new UPS. I have 460W HP ProLiant ML380e (Gen8). The problem is that i'm not well versed in UPS technology.

My main concern is that I don't know what else do I have to keep my eye on other than does it have enough Watts? For example... if I go to my boss and suggest, that we buy Eaton 5P 850iR for 450, then she might say something like this.. "what about this ? It has enough Watts to keep things running right?" Now i could of course read a list of things that the more expensive UPS can do, that the cheaper can't, but I don't know how to separate "vital" features from "nice to have" features.

The thing is that we don't get huge amounts of black/brownoutsand (though i haven't measured it closely) and I know that I have a weakness for new shiny IT stuff, so Eaton 5P might be a bit overkill... compared to......