Butterfly gag is an evil device. No internet link for one, unfortunately... though I am sure someone can help with that.

It has three bits - one goes behind the teeth, the other two go over the teeth and under the lips. You then inflate it - all three parts inflate and push together making a very effective gag.

For beginners, I'd suggest a ball gag and then work up to a more substantial one. Ball gags are easily the most comfortable hard gags (i.e. not cloth or tape based) you can get.

It helps if you get the right size as well. Too big and you can cause aching jaws, too small and they don't work so well.

Inflatable gags - you may be right about them not being for beginners. Though I have heard of them referred to as 'trainer gags' as you can inflate them to a required level which is comfortable for the sub and increase it in future sessions - thereby building endurance. Perhaps what was meant was not for inexperienced Doms. Probably Ok for an experienced Dom to use on an inexperienced sub.