That being said, I'm a straight up Electronics International fan. The wiring harness will be more complex than the '275, but you can get more systems programmed also. Compare the available options for each instrument and see if you need the extras from the CGR30P.
What aircraft are you installing this into? I'm assuming certified and not experimental? I'll have to do some more research but I'm not sure the engine side of the 275 is certified primary (the flight instrument side is) whereas the CGR30P is primary.
They honestly look pretty similar to me. I guess the difference would be in Garmin’s ability to be more than one display, but if it’s your primary engine display then I don’t know you can shuffle off the engine screen.
No experience with the Garmin, lots with the CGR30P. Sold and installed lots of them in Super Cubs. Like flying behind them as well. I'm a dealer for EI and just got notice of a $300 rebate on the CGR30P if purchased between April 1st and April 30th.
I love my EI instruments!! If I have a problem or question I just call them. Someone answers the phone!!! Then the will listen to me! If I need a part it is in the mail the next day. Great company with no you are only a pilot BS!! DENNY