RE: FUTABA Telemetry
+1 on the fuel gauge. Load of crock.
Engine temperature sensor - why would I need it once off the ground. Maybe indicate lean run? Well engine note changes long before temperature came into play.
Receiver battery warning - watched it in action on a A9 yesterday. NiMH pack lost a cell somewhere in flight. Pilot pulled plane onto knifeedge and the voltage dropped below the threshold Problem was he knew he had an issue before the warning went off since the plane was sluggish on the rudder. His plane did not make it back, it went into failsafe and circled into the bush. at idle. Very little damage but he's parting comment: "So much for battery telemetry..."
Now he hates the radio even more (Says its too heavy and ergonomics is poor - his words not mine)
Theres simply no substitute for proper pre flighting and regular maintenance. Telemetry is just an added expense that adds complexity and in fact raises the power requirements of your on-board flight system.
I'll say it again. Currently its poorly executed and gimmicky.
If manufacturers are serious about telemetry then battery early warning should monitor the change in voltage drop under load over time to decide if the battery is being overloaded or a problem is developing.