There's a massively long thread here if you want to read about the science and other people's experiences: https://www.e-cigarette-forum.com/f...er-flow-flavor-saturation-and-nic-hit.561226/
I read that thread a while back before I bought Cellucotton. It's way longer now but there is a lot of info in the first 10 or 20 pages if I remember correctly. Health issues and the chemical processing were I believe discussed and I also did my own research on it.
I consider it safe enough to vape, but that's just me and YMMV as always. There are potential risks with almost everything in vaping and over the years I've seen a lot of hysteria about stuff. In the end all we can do is make up our own minds about things and run with that.
I have been using both Cellucotton rayon and Koh Gen Do for the last year or so. IMO both perform very similarly and vape better than regular organic or non-organic cotton, cotton thread, hemp or silica.
You need to stuff noticeably more rayon in a coil than cotton to get good results, so I use rayon on stable builds with 24 or 27 gauge Kanthal. With softer wires like nickel or titanium I use KGD. None of these gives me any funky tastes even the first few drags.