Here's another great rc receiver from Fr-Sky, the RX4R! The FrSky RX4R is a standalone receiver with all the functions of X4R, but with some upgrades. The RX4R has 9ms PWM output latency, less than that of the original X4R in high speed mode. You can even add a second backup receiver in case the first one fails with the supported redundancy function on the RX4R.
This receiver is super-small even though it's features and performance have increased compared to the older models.