The Sterling Hollow Block is a very good autoblock\prussic option as well. I use it on rocks as well as trees.
What is a "Variable Controller system?"
My thoughts on rapelling the 20- 30 feet from the tree are "Keep it Simple". Extended ATC & autoblock\prussic,and you can stop at will, get all your Stepps or Sticks untied on way down and it's lightweight.
Grigri2 works great too, but I wouldn't go buy a $95 grigri just to rap 20-30ft out of a tree, besides it's heavier than an ATC & hollow block. However, with a few extra "bits" you can rap down rope & set tree up for SRT with grigri. I have been rock climbing for 9 years and a majority of the injurys\deaths I read about happen during the rap down. I know, I almost became a statistic 7 years ago & had I not "double checked" my set up I wouldn't be typing this. With rappelling, simple, & safe is good. Oh yeah...
Check, check, double-check.