I've never done a side by side comparison. The RNC obviously has a disadvantage over "brand name" comps because it's got a wall wart and limited metering, etc. The C300 is also lacking a bunch of control, but it's a lot easier to haul around.
In terms of sound quality, the RNC and C300 both don't have a sound to them. I've never used the BSS, but Klark and Drawmer certainly have their own "thing", which isn't necessarily bad. I've got dbx in my A FOH because I like that sound, but if I'm compressing extremely hi-fi acoustic sources I don't want it, and personally I'd be happy to reach for one of these two budget comps. Were I buying something to take out to shows where other engineers would be using it, I'd probably find something a little more "rider friendly".