I personally have an RT'ed A5, and I love it.
I love that I don't have to use batteries (or worry about getting my marker wet!), I love the physical kick you get from firing full auto, I love how you can simply turn a screw to fine-tune your bursts and ROF in full auto, I love the simplicity! I'm not one for using full-auto often, but I 2-3 ball burst a lot and I take comfort in the fact that I can always "rock and roll" if I feel like it.
I just plain love mechanical setups.
What about you? What do you use, and why? Discuss...