So one quick note on using the D2 as a back-up: The D2 was primarily designed with the portable usage in mind, so that pilots of certified aircraft and especially renters can bring it with them into aircraft that aren't very well-equipped. The thing it gives up over the permanently-mounted EFIS-D6 or EFIS-D10A is actual airspeed, pneumatic altitude, and magnetic heading. The EFIS-D6 / D10A can show you those beause it has the requisite pitot and static connections and magnetometer. With the D2, the speed, altitude, and direction are GPS-derived. Useful information, for sure, but if you don't need the portability of the D1 or D2 you'll get a bit more utility in a homebuilt out of a EFIS-D6 or D10A.
As for "does it work well" - I'm obviously biased, but if you haven't seen the Pocket Panel
feature pages, some of the reviews featured there might help.
We had a rebate on the D1 for a while, but lowered its price permanently when we came out with the D2. There are no rebates or sales going on at the moment. The D2 is priced at $1425.
Michael Schofield
Marketing Manager
Dynon Avionics