Hi Colin,
I use ACP for automating my own image capture at home and at star parties and have been very happy with it (apart from the expense!) We also use it at SRO for fully unattended/automated operation and it works very well for that.
I evaluated CCDAP and CCD Commander before choosing ACP. SGP wasn't available at the time. It looks pretty good but doesn't support all the features that I need. Maybe one day if they keep up the rate of development...
I use FM4 and haven't really explored the new features. FM3 was perfectly adequate but I figured Steve Brady deserved some cash
There's a new slower but more precise focusing method in FM4 that I should try.
Glen: IMO, parfocal is just a marketing term (and "parafocal" is just a spelling mistake.) Filters that focus within the CFZ on a f/8 system won't necessarily do so at f/5, and that's assuming you believe that anywhere in the CFZ is good enough.
Cheers,
Rick.