It's a laptop holder.
Funny thing is I rarely code on a laptop anymore. I find a tablet to be so much more portable and I'm adapted to the touch keyboard. So I could use a park bench or sit on the ground and still be productive.
One question I have is not in the FAQ. How do you prevent theft if you leave it strapped to the tree when you walk away to use the bathroom?
I try to find a spot that either has a real toilet close by, or a place with a foresty area where I could pee in the bushes. A bonus is if I can keep line-of-sight on my Tree Table. In any case, I leave the tree table attached. No one is going to bother to steal it, it looks too unusual, weird, intimidating.
I could also ask someone else in the park who looks normal to watch my stuff, but I have never found the situation to be critical enough to make such a request.