I tested vertigo VSC 2, APi 2500 and STC 8/M and bought STC 8/M
it was my first outboard comp. before I decided to keep it, I did a lot of tests with the same files on all 3 machines and after about 2 weeks of very intense testing the clear winner (to my ears) was the STC 8. none of the other comps had such a deep and crystal clear (in hara mode) sound especially with higher gain reduction levels (still never used more than 3-4 db GR normally between 1 and 2 db). for a little coloration and to tame harsher HF the KI mode can be usefull allthough I don´t use it too often. Even the not much liked limitter can be usefull.
maybe the api is more versatile and the VSC sounds more "natural".....but as I had only the money to by one at that time there was really not much to think about for me after my tests so I purchased the STC 8/M....of course I would have loved to keep all three
now I own more outboard and will sell maybe some of it, but the STC 8 is a clear keeper! I have to add that I use it with the side chain and it makes the STC 8 much more versatile than it is without!