I don't think it sounds anything like any compressor I own.
I spent several hours one day auditioning the "Vocal Rider". Was never as happy as when I took the the time to automate my own vocals....which usually doesn't consume tons of time if I've recorded them properly. For me, on the label mixing front, it sounds more natural to do it myself.
However, I did find one amazing use for it......When we are cutting vocals, I'll slap it on the playback, so I don't have to try and keep up with the singers dynamics, and it gives me a much better representation of what the vocal is going to do during the mix phase, and I can spend more time focusing on the performance, not trying to balance the "raw" vocal track when we're trying to make performance decisions.
I have used it on some tricky sections in a couple of tunes on bass, and it was fantastic. Still had to go in and manually make some adjustments.....However it wasn't as noticeable (in a bad way) to my ear as it is on a vocal track. YMMV