I trust this doesn't sound too demeaning, but I don't like any of the Comet antennas, and for good reason.
If you read the fine print, you'll find out they rate their mobile antennas against a typical handheld radio antenna. Read that as a rubber ducky! If that wasn't enough, they are not very sturdy. While they do make models with NMO mounts (the PL259 types are junk), they won't fit on a Motorola NMO. Go figure!
The most popular dual band antenna out there is the Larsen NMO2/70B. Properly mounted, it will out perform any Comet antenna. And it's less money!