Aspen Avionics AT300 is designed to be a drop-in replacement for a vertical speed indicator, but you'll get a lot more usable information in the cockpit when you couple it to your GPS; by Rick Lindstrom.
Do you need to run your engine for the DAR? How does using a certified engine and prop affect your Phase I test period? How about the gray areas regarding dual flight instruction? DAR Mel Asberry gives you the straight scoop.