I feel much safer in stands I build, mostly because they are bigger (I like to stretch out my feet).
The most recent one I built is 2x8s between three trees with 2x4 decking across. The 2x8s are secured with 4" lag bolts (stainless steel), 4" wood screws and 4" nails. The decking is secured with deck screws, the whole thing is stained to protect the wood, and there are safety rails (poles that I cut making shooting lanes).
Another stand that I built only uses 2 trees, it was wobbly if you got near the edges, so I ran airplane cable from eyebolts on the corners of the stand up to lag bolts in the trees.

The only saftey concerns that I have ever had was home-made ladders, now I keep my eyes out for any TV tower that I can get my hands on, lash it to the tree with airplane cable and I'm fine.
Much safer than teetering on a tiny steel platform chained to a tree trunk.

Obviously my stands are different than home-made climbers or other portables, but I can stand up and stretch, sit down cross legged, basically get comfortable so my muscles don't seize up. I'll get pics of one the next time I'm at the farm (maybe this weekend).