a post on GS
"This is Oskar at the Softube Support. Thanks for reaching out!
The FET Compressor Mk2 is completely rebuilt, based on another hardware version, and modeled differently. There should be an upgrade path available for you on the website.
There is however no crossgrade from the NI versions. They are based on the same emulation, same code, but are new plug-ins. And they have different feature sets.
The VCA also has new gain staging. So they will behave differently."