I used one last year a couple of times and it did wonders for the mosquitoes, but didn't see any deer. Coinsidence?

If they can smell the thermacell then they will have already smelled you. You put off many times more bad odor than a thermacell will and to a deer you stink a whole lot worse than that thermacell ever will.

I used thermacell last year andhad no problems seeing deer while using it.

I'm very carefull not to contaminate my hunting gear with harmfull odors. I don't even gear up until I'm out of my truck and ready to go into the woods. I also use scent elimination and containment, plus various cover scents around my stand. I'm pretty successfull considering the amount of time I spend in the woods. No monsters to speak of, yet.