This is a great little tool that I would recommend to anyone because it sounds good, takes up very little CPU and best of all has zero latency. All of the modes: Opto, FET and VCA sound convincing to those types of hardware designs, although they are not modeled after any particular build. I actually do have alternatives for each compressor mode, but because of it's small footprint I usually start with Multicomp, and a lot of times I prefer Multicomp's character over the alternatives. That amazes me considering the alternatives take up 3x the cpu, have latency and were more expensive.
My only complaint is that parallel compression is best done with oversampling turned off, due to the fact that there are slight phase inconsistencies with the original signal and the compressed when oversampling is engaged. With oversampling turned off parellel compression works great and I personally have never heard a difference with oversampling and usually have it on "just in case".
Overall I think Multicomp is one of my best plugin purchase.
UPDATE!!! I just got an email from Saverio with an update that fixes the phase consistencies in HQ mode.