Rayon is awesome! Superior to cotton as a wick in every way possible. It is very safe to use and I highly recommend giving it a try.
Check out the Rayon
thread to have all of your questions answered. JeremyR has done tons of research on it and there are many of us who use it exclusively... and will never try anything else! LOL
Rayon Wick: Better Flow, Flavor, Saturation, and Nic Hit
There are also a ton of tips and tricks there that will show you how to properly use it. Everyone over on that thread is very friendly and helpful. If you have questions or problems with rayon, I promise that you will get sorted out over there.