I should be getting an Ampeg Opto-Comp in the mail soon for my small board. I'll let you know how it works. I tend to prefer fairly light and natural compression and I don't want to have to deal with a lot of knobs.
I like the Keeley Bassist because I hate too many choices in a pedal. I essentially set everything to noon, which would equal a relatively high threshold, but one that still engages, and a 6:1 ratio. It cleans things up and makes them sound more orderly, but you can't really tell that it's on, there's just less bashing and booming.