Best brickwall limiter on the market, bar none. I use it mainly for about 4dB of final gain. It also adds excellent glue and a bit of warmth too, if you don't push it beyond what is reasonable. I've tested every mastering limiter on the market. This buries them all... which is a bit surprising for IK Multimedia. It's a hidden gem to be sure.
I was confused at first; the output ceiling is also a level control. When the input level matches the output, the gain is linear (and will cleanly null out) until you do hit the ceiling, and then the clipping is nice and natural).
I frequently use this in place of the stock limiter on Reaper's track input chain (instead of a channel strip) when I want peak protection without coloration because level-setting is as simple as it gets.