I have the 520c in my parents' home theater along with 4x 580 towers in a 5.1 config.
The 520c sounds good, in my opinion. It can handle getting loud and blends in pretty well with the towers.
Yeah, it doesn't measure perfectly on a klippel test, but it does handle SPL plenty fine for our use.
Could we get better sound with something else? Probably. But for the <$100 we paid for it, I'd say its pretty good value.
For the record, the receiver we are running is the Yamaha RX-V6a. It has plenty of amp power, but only "OK" room correction in my book.
Of course, if I was to build a system for me, I'd be using custom 3-way speakers, but I don't have the space in College Station...