Hi Roger,
Again, I don't have a DDM (but I do have an ASA scope), but once the mount is tracking to within an arc second or two, the atmosphere takes over. Ask any imager, there are some nights where you just can't seem to make things work, then you actually look at the stars and see the wild scintillation characteristic of really bad seeing. No mount can fix that (at least in the amateur sphere).
So your question is, do I stump for the DDM and hope I don't have to guide, or do I get a PMX or AP mount and live with the guiding?
I have a PMX, and apart from some problems which did go on for quite a while, it has been great, once I replaced a dud motor. You can PEC train these things to very small residual errors and set up sky models to remove most of the pointing errors, but still most imagers guide anyway. Once you have made that decision, i.e. to guide, then PEC isn't really necessary, a decent polar alignment is all that's required. Even better at long focal lengths is to use AO and only bump the mount when required, if you PA is good, that won't be very often. One of the drawbacks of using a Newtonian scope like the ASA N12 is that you have very limited back focus from the corrector, so no AO for me
SO direct drive or not, probably not the question you need to ask. What you get with your mount is also worth consideration. I'm not sure what you get with the ASA mount, but with a PMX you get a lot of software as well. Then there's support, the SB guys run this forum thing, which is frustrating when you have a problem, not sure about ASA, though they have a rep in Melbourne, but I suppose Bintel or Peter are the SB reps in Aus.
HTH
Stuart