GWS do a failsafe that works fine.

I have flown with Futaba 138 RXs and the GWS FS-1 Failsafe Unit and had no problems.

I personally like having advance notice of a poor link with the model [ i.e. getting glitches] that PPM gives. I find the sudden lockout that PCM gives unsettling.

Some of this comes from a background in RC combat where you have a large number of TXs spread out along a line and interference is an expected event.