I have the Sundstrand ECU in my 980 (which was the original ECU design from the factory), along with a Keith freon air conditioner. I think it's the best system available for the Jetprop Commanders (840/980/900/1000).
The Sundstrand got a terrible reputation when new for early failures. However, the recommendation for checking the oil was something ridiculous, like every 300 hours.
Per Bob Mays' recommendations, I check the oil (add, really, since that's all you can do) every 25 hours, and change it completely every 300 hours. Furthermore, there is a service bulletin from the 1980s which adds some ducting to give the unit additional cooling.
Finally, never, ever, ever, use the MAX FLOW switch. It's fine to use it in a 690/A/B, or an enviro-equipped Jetprop, but not with a Sundstrand.