I want to share with you my recent experience with Davtron. I have a
Davtron M655 (http://www.davtron.com/m655.html) multifunction indicator
that shows voltage, OAT, pressure altitude (from the encoder) and it
automatically calculates and displays the density altitude. The unit
was installed in 1999 when my Traveler was restored by Airmods NW.
Recently the M655 started to work only intermittently and it finally
stopped working all together. I sent the unit to Davtron for repair.
According to Davtron's website they charge $45 flat fee labor plus
parts for repairs outside warranty. To my surprise, I received an
email two days later saying they found a defective component on the
circuit board and they'll fix it for free. 6 days after I shipped the
unit it was sent back to me in priority mail. (Davtron didn't charge
me for shipping either).

Upon re-installation the unit continues to work only intermittently,
although a bit better than before. I shipped it back the second time
and it was back to my house in 5 days, again w/o any charges. This
time the DB15 connector was replaced and the unit had been working well
since.

I have to say I'm extremely satisfied with Davtron's support of their
product. These people really stand behind their product!

If you want a gadget that will make it easier for you to set cruise
power the M655's density altitude function is great. Just look up the
density altitude number in the "standard temperature" column in your
cruise chart. No E6B or temperature correction needed since density
altitude has already taken that into consideration. You can also see
what your encoder says about your pressure altitude to ATC radar.