Since the thread is alive (again), my two cents about opto-compressors:
I play acoustic music with vocals, mainly, and I use two LA2A-clone opto comps.
Three reasons why I bought them, and love them:
They are delightful for acoustic music, in that their very design (the photo cell sensor plus tubes) makes for smooth yet effective compression.
They don't "sound" aggressive the way solid-state comps can, unless you flatline the compression level, yet you realize they absolutely bring the tracks forward (and loudly) when you dial them up...your meters will tell.
They are intuitive. Two main dials, one is compression level (I believe ratio is set at around 3:1) and the other is output to the mixer/recorder.
They are "musician's tools" in that you can try/dial things in with no effort and just listen...no ten controls to deal with, no deciding endless settings.
Mine are hardwired in right after my pres; I use them straight in as I record, and they can either compress to taste or just pass the signal through the path for some goodness.
They embrace the beauty of simplicity. As mentioned, two main dials, and a set comp ratio that varies in level...that's it. They have a switch you can throw to put them in "limiter" mode, but that's as exotic as they get. They do what they do well, and if you need hard-knees, many ratios and such, optos are not for you. Mine are the AudioScape replicas (3-rack-units like the originals) with the big VU meter which you can see across the room.
BTW, I second zizjaturtle's post, re: help. If we can't be bothered to answer a question, why have the forum?
Google can't give you user experiences, tips or add the 'human touch' to what you are asking. I like to think that's why we do this here.