I don't know how many are familiar with the MicroEncoder from Rocky Mountain Instruments http://www.rkymtn.com/ , but I have it installed in a conventional panel and I like it a lot. It combines digital airspeed, altimeter, VSI, and OAT. I have the readout set for KTAS and it corresponds very closely with GPS runs. The airspeed trend indicator is useful for power setting. I find I refer to it in cruise and switch to the analog airspeed for takeoff and landing. I have the compass module installed but haven't activated it.
 Potential backup...?  -Bill Wade