I've used Eagletree loggers for some time now, which do similar things e.g. measure voltage, current, watts, RPM, temperature etc. etc. I've never used the telemetry option, I just use their micro logger device which records to memory, as I find that does the job for me.
A lot of companies are also integrating data logging and telemetry into ESC's and receivers, although in the case of telemetry, it's on 2.4ghz generally, which isn't much use for subs.
A chap who comes along to the Dive-in events builds his own radio sets with telemetry. He posts on here sometimes, so perhaps if he's reading this he can chip in.