I would like to use a Lipo because of how they perform. I have 4.8v batteries, but would prefer not to use Nimh, or Nicd anymore. There are a few benefits to having an opto kill that I like. When toggling it on and off with the TX switch, you can test and hear the plug spark, so I know I have it working.
The RCxcell does like a good unit and I am leaning toward one of those unless I hear bad things otherwise.