I believe I bought it when it came out, so it will work with X2. Concrete limiter is a really good option as a single band limiter. I use it in channels, not on subs or the master sub - its the go-to tool unless I have to control a real specific area in the spectrum - then on channels its the L3 LL, but then I have to work to tune that little hoober doober in.
Mr. Anderton took the time to figure out how to use it when you need it to set it to control certain frequencies ranges differently. He paired it with another tool in Sonar and side chained multiple instances of CL with it. Sorry, don't remember the specifics to this.
For normal instrument playback, its pretty darn transparent. I'd buy it again, and I already own L1, L2, L3 and L3 16. Its just a really good - well designed limiter.