Here are the names of other products of which I'm aware that are designed for wide field astrophotography:
Purus - German made mechanical clockworks drive - out of production AFAIK, and in the lower price ranges - needs to run for a full minute without adjustment to reach a correct stable drive rate before the exposure is begun
Byers Cam Trak - discontinued, sought after, made by a premier maker of professional telescope drive gears - electronic
Kenko Skymemo - still available new for about the same price as the AstroTrac TT320X - electronic
Kajers 7700 - discontinued AFAIK - electronic
Takahashi Teegul Sky Patrol - available around US$1000 - electronic
Astro Kits (
http://www.company7.com/library/astrokit.html ) - out of production, few sold, around $125 new - 4 AA batteries or DC supply
Orion Min-EQ Tabletop EQ mount
http://www.telescope.com/control/pr...pods/~pcategory=accessories/~product_id=09055
- needs one of two available electric motor drives (with or without hand correction paddle) to track for photography. Base unit about US$60, and motor setups at US$45, or US$73 with hand paddle.
Book:
Jim Ballard - Handbook for Star Trackers: Making and Using Star Tracking Camera Platforms, Sky Publishing - appears to be out of print, but used copies around
Of course you can also find a number of new or used equatorial telescope mounts that have, or can be fitted with drive motors. You'll have to do your own research on the suitability of these mounts for photography. The important features are some way of polar aligning accurately, and a drive system with a proper tracking rate and as little periodic error as possible. (Google 'periodic error' so that I don't have to write a long explanation here.)
I have used a hand built straight bolt drive, an Astro Kits motorized curved bolt drive, and a Synta EQ-6 telescope mount for my own wide field astrophotography, all with very good results when used within their limits. The Astro Kits and Synta work well with up to 15-20 minute exposures with my 180 f:4 and shorter lenses. That's getting to the limit for sky fog where I typically shoot anyway.
The current trend in amateur astrophotography is DSLRs with computer driven and timed multiple short exposures (up to about 5-10 minutes), then stacking in the computer.
Lee