The 5us receiver sensitivity spec is probably a misprint... perhaps they meant 5 uV (equivalent to -100 dBm). Not a great spec for a radio, but probably OK if you only need a mile or 2 of range and it is free space between antennas.

Receives are commnly specified as some quantity of signal required at the receiver input (usually measured in dBm or uV) to acheive some specific metric of performance depending on the application. eg.

eg. 2uV for 3% rms full scale error.

Alternate meteric for recivers are:

Like % full scale RMS servo error for RC

1e-6 BER (Bit Error rate) in data communications (applicable in PCM RC).

12 dB SINAD for voice communication.