I have an A-199, and this is the little I've worked out about it so far:

* It seems to be very quiet. if I plug my VCA's output directly into my breakout box, the signal's very loud. If I plug the A-199 in between them, I'll have to crank up the VCA to compensate. This isn't a problem, mind.

* The spring reverb tank picks up the mains power conversion hum very easily. I've got mine sitting on a box next to the Doepfer case, rather than leaving it *in* the case, and it sounds fine, although it looks a little awkward. One day I'll probably get a custom case and install the DIY bus board which uses an external power brick, which I'm guessing should fix this issue.

* Remember you can pluck the spring itself to get those kinds of effects you're after. It looks like a very subtle and sensitive device, as you can never see any physical movement even when it's making quite loud reverb (at least, I can't), so plucking one of the springs manually may not be good for your ears, but it does make interesting sounds. This is the other reason to keep it outside of your case.

I could be misremembering any of this, or getting superstitious, so anyone feel free to correct me. :)

Better information about the A-199 is available at http://navsmodularlab.blogspot.co.uk/2011/06/doepfer-199-spring-reverb.html courtesy of Navs.

Anyway, it gives an interesting metallic sheen to things, so I'll certainly keep it and continue to experiment with it. :)

All the best,
Zoë.