A while back I did a personal shootout at home between the RND MPBII, NG Bus Comp, and the Bettermaker Masting Comp.
Obvs the RND and Bettermaker are specifically mastering compressors, and I indeed found them to have much more in common sound wise with each other than the NG did with either of them.
With an existing mix I found I could shove the RND and Bettermaker at the end to improve the mix without affecting its whole balance. The NG drastically altered the mix and stereo image in a 'pinched' way thinning way I didn't like, and didn't respect the low end of the source material. I tried for MANY hours to get the same kind of pleasing results I got from the RND/BM with the NG, couldn't even get in the same ballpark. Tried all 3 on the drum bus, same thing - even the iron options didn't help me get anything out of the that box I couldn't entirely live without.
I use a Wes Rhea when mixing ALL the time to add a bit of saturation and lift, usually bended in parallel. I have 2x Rhea now, as love them on drum bus too! I have 2x Mimas too, that am saving for a rainy day and haven't been using much yet. thought of a Dione, but my experience with the NG put me off.
maybe all that proved is that I prefer Mastering style compressors and Vari mu's for mixing, and that the classic SSL sound is not for me - But thought I'd share these results.
RND vs BM, RND sounds a shade better, sounds amazing down low without use of filters, and I love how RND sits a snare in a mix in a way that makes it sound great without muffling it, but the BM had recall and a load of other useful features I wanted, so sold my RND and have a BM now.