I have a EDM760 in my FT337GP. It's great and I now would not fly without it.
It would be nice to have some of the 800 series features, but you can't always have everything. I can always look at the power charts to get % power and I would expect the charts to be more acurate as they account for temp. etc.
My setup has FF, OAT, cyl, EGT. I did not get oil temp as all the other gauges are working.
What do I like about it. I have set the alarm levels lower than red line and I get good alerts when the cyl temps are starting to rise on a long ground hold. I then just turn into the wind a bit and they go down and you can see it.
When on decent, it helps you manage keeping the heat up and avoiding shock cooling.
I liked the fuel flows, but I think I need to rework the hoses as the runs on both sides of the sensor are a little shorter than they should be and I think line turbulence is causing irregularities. In fact I get zero FF most of the time.
I have it interfaced with the Garmin 530, but have yet to actually use that ablility. It would make long distance fuel management better. I will be working on that as yet another a new project.
It recently helped pin point the need for baffle rework.
Lean find makes leaning very easy. I only run 100 ROP and always use 55% to 65% power setting and it makes getting there fast and easy.
I like the data logging a lot. It is great to be able to look at all the data after a flight. I have all the flights on my PC and the look back ability is very nice. I use the SAVE utility that comes with it, and bought EGview. That is a great piece of software, much better than the spreadsheets I was using. If you are interested go to
www.egtrends.com and take a look. BTW, that software supports a number of units.
When on the first flights with a new rear engine it was great to go back and look at the flights and look at all the temps. One comment I have heard is that with the logging, warranty issues become difficult for TCM to dispute.
What don't I like. I wish it had an alarm for OAT so the need to watching for ice could be alarmed.
Pay back - long for sure as the units are not cheap. Try negotiating for a discount. Mind you if you take the 5 year view and don't tell your wife, the cost sort of disappear (unless you are raiding her food budget).
Final word. I like it and I think it has improved my engine management and makes me feel more comfortable that I know what is going on in the engine.
My 14 cents worth.
Regards - Dave