As reported by the others, the glass mount type are not worth your money except for vehicle to vehicle in close range.
Here's a link to the type I installed on our Georgetown.
I mounted it on the driver side of the Georgetown about 6 inches behind the drivers side window frame. I determined the height of the mount, based on the height of the actual antenna. I wanted the top of the antenna to be 6 inches higher than ANYTHING rigidly mounted on the roof so it would act as a "curb feeler" to let me know how much vertical clearance I might have....such as under the roof at gas stations, trees, and especially clearance issues at the various parks we travel within.
The reception of this style is satisfactory enough for my needs to be able to monitor others, have conversations within a respectable range, but most of all act as a "curb feeler" against any rooftop damage. If you know the term "curb feelers" you know we're from the same common time in history.