[...] since like to hang it from their mouth when they play the guitar. Does anyone know a model that would be good for that?
The 84mm is quite light but...
...it doesn't have a manual battery so...
if you are playing electric guitar, the amps and speakers trigger it on all the time... it gets really really hot!!!

ouch!
and more... that can't be a good thing for the lung apparatus, battery & atomizer
Even away from amps and speakers, I find that any brisk movement triggers it... draining the battery... and also making it kinda hot sometimes!
?--->
Are all automatic batteries that sensitive?
@antism
Do you have a manual battery? If not, have you experienced the constant triggering?
That said, I think a manual battery is the way to go, guitar or not!
I was looking at the titan or joye510 for my next purchase. Is it that much heavier than the 84mm?
As for holding a manual in your mouth... well...
unless you can do freaky tricks with your tongue

...
you couldn't
vape while playing guitar with your two hands
Cheers!