Re (Windscreen (glass mounted) antennas for mobile network work very well,)
From my experience with a Sprinter Campervan, the best thing about this type of Antenna is you don't need to go thru the Firewall/roof/Door Gap, to get the aerial lead to the phone. I think compared to a Broomstick aerial on the roof of the RV/Vehicle, its a Chalk and Cheese comparison ( From a user of both setups). Ditto CB Radio.
Would definitely recommend them, its the difference between having communication or none. However height is a significant part of the comms link when remote bush ie on top of the Winegard TV aerial on the Caravan or above the roof of the Cruiser.
Our Antennas are similar to the item below, come in 2 types, 1 You can screw off the aerial from the spring base, in case it breaks due to hitting a tree branch and 2 complete unit. break it and you replace, along with the cabling in the vehicle.
Really cannot say, as I have not done a test, all I know is that with the Mob Phone Aerials, I can talk and have data access and friend in the same location without an aerial has no comms. He plans on having a similar setup next trip.