My set up doesn't have a prop brake (I think).  Hacker A30-XL with companion controller.  Hubin timer.  The prop free-wheels to landing after cut-off.  It doesn't seem to hurt, except maybe the glide is 1/4 lap shorter because of prop drag.
Where is the prop brake implemented?  In the controller?  Timer?   On my next electric power package I'll pay attention to the prop brake feature.

Floyd

Floyd, do you have a programmer for your ESC? I assume you are using the Hacker controller? as Igor said, its programmed into the speed controller, some are not programable. And your observation about the shorter glide is pretty much the only issue in AMA rules. However I think there is something in FAI that requires the prop to stop prior to the "landing" begining?
( this is Not a knons fact, just based upon what I have read online)

Floyd:
First off I have not direct EXPERIENCE with the Hacker, nor do I recall seeing anyone post anything on the forums about them - thats the grain of salt part.

I went to one site that sells Hacker ESC's and they talk about the ESC and BRAKE being programmable via a USB cable link.  Did you get this system from RSM?  Went to the RSM site and they list a USB Programming link.

Thus my conclusion is that if you want to turn on the brake, you need to get the link (about $15), hook it up to your PC and program it.

The biggest practical problem I can see with "no brake" is that it will put limit on what you can do when landing in windy conditions - no stretching the glide!