refrigerated air driers?

who knows what about these? I see a couple on Feebay I am looking at but the ones I seem to be interested in are less capacity than my compressor produces. Do I size a drier based on that or actual usage "at the moment"? The ones I found are supposed to be good used takeouts, I believe taken out, because they run on R12. The place selling them seems to be an industrial liquidation company. Would I be ok if I ran 2 of them in series?
Would I be better to plumb them between the compressor and tank? or at tank outlet? or in the case of my sandblast cabinet would I put one right before the air line goes into there?
I have a 2 stage compressor that as I remember it's around 17.5 cfm at 175 PSI.
I have an Emglo, (now "Jenny") 5hp 80 gallon 2 stage 4 cylinder pump.
if the unit I am looking at says good for 10 CFM/150 PSI would it throttle airflow down to that level? Or would it just not "catch" all the possible condensation as it flows thru?
(I will have to check and verify my compressor's outlet)