The optidrive on a Revo is not a failsafe in the true meaning of failsafe. It gives you a low battery indication but will not lock up the brakes if it loses the signal from the tx or if someone else gets on your frequency.
I used Venoms and was very pleased with them. They are somewhat small, easy to set-up and not too expensive. Using Spektrum now and it's built in, can be a little tricky to set up though.