Many of us have used the ThermaCell in our observatories for over a year now, with no ill effects on the optics on our equipment. It doesn't emit "smoke", rather a small amount of vapor.
Everyone should use whatever mosquito protection they feel comfortable with, so they can enjoy the beautiful night skies. For me, it's the ThermaCell.
-------------------- Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Pentaxes; 5XW, 7XL, 10XW.
14mm Meade 4000 UWA
TV Panoptics; 22, 35
Garrett 20x80 TWP setup