I'm no expert on this, but I believe there is more to buying a UPS than the obvious sizing calculations, and there are even many grades of "AVR" (automatic voltage regulation).
A good read are APC's white papers:
http://www.apcmedia.com/salestools/SADE-5TNM3Y_R5_EN.pdf and
http://www.apcmedia.com/salestools/VAVR-5WKLPK_R0_EN.pdf
Be aware that most consumer UPS are sold for home computer use. Home computers typically use switching type power supplies, which don't care about the waveform shape. The HR20 is probably powered like a PC, but if you're also intending to protect your A/V receiver or plasma TV, you might want to invest more dollars to get a true sinusoidal output (I don't know which units really care and which don't). APC makes units specifically aimed at A/V use, and they are specced as producing a "true sinusoidal output."
Note that just having an "AVR" designation may not be getting you what you think. APC's lower end AVR units have boost only features (90 volts becomes 103), while their higher end stuff has both boost and trim. And then there are things like output voltage distortion, etc. etc.
It's one thing to filter the power, another to condition it, and yet another to supply it from a battery. Personally, I ended up getting a Tripp Lite dual online system for my A/V system, but I also needed to condition my backup generator's power. The dual online system protects my equipment, and let's me run it off the generator (which has really dirty power) for extended outtages.