I'm only a novice tree climber, but I've been a rope rescue technician for many years. I guess I did things backwards, but my first experiences with tree climbing were SRT-type. (I think that's right - Someone correct me if I'm wrong) I tie an anchor at ground level, climb using ascenders and then switch over to decender to come down. At least that's how I did it. There's definately more to think about, more gear to haul, handle(and drop),and unless you use a prussik loop as a self belay, I think there is a greater safety risk for a novice using an 8.

I use a rescue 8 all the time, because that's what I'm familiar with. I'm learning different methods now, so I can see why some people either love 8s or hate them. I carry mine because it can be used as a rappel device, belay/lowering device, and a rigging plate.

As for the weight. My Kong 8 (alum.)weighs only a couple of ounces. I do have a stainless steel piece that is QUITE HEAVY - but it's rated at over 11,000 lbf!

IMO, use what you are comfortable with, but it never hurts to learn alternative methods - I am.