I found a nice videos about different types of ring gags with short reviews. I suggest you to go and check it out
On this video you will get some detailed information what people likes when using mouth gags. We all know they're nice to spice up our bedroom activities. Watch it below
The last video of this short series of gags are O Ring Gag which is awesome for all BDSM lovers out there. If you check the link in description of the video you can find some nice deals to get your favorite one.