It’s been a while since there has been an update to this, but that might be because there is not much to improve on. You may have noticed most of the plugins I own are from the “big-name / expensive” guys, but PSP is that rare indie exception.
Those graphs look pretty clean, a might too clean I would say. Not that I have a 1950s RS56 laying around, but I’m going to guess it was a bit more noisy and added a bit more distortion than this plugin. So — if you were dead set on perfectly re-creating the character of this vintage tool which was first used in mastering for vinyl cutting, you will be disappointed. You know, since you are obviously so familiar with that sound and all.
The interface is pretty straightforward but you have to pay attention to the controls, there are a lot of (non-intuitive) things going on. This is for someone who wants to listen their way through cleanly touching up a sound. It’s subtle. (Or musical. People always use that term—it just means you can’t do anything really drastic to the sound.)