The only deal-breaker for thru-the-glass antennas is if you have metallized windows in the vehicle. And that is not always easy to determine... there is at least one other thread here on RR regarding this.
But I have always used a glass mount antenna with the scanner, and it works fine for what I want... which is a broadband antenna with a reasonable listening range. When I'm mobile I don't care to listen to something two counties away. My main interest is within 5-20 miles of my vehicle. Not as good as drilling a hole, but without the drawbacks. Some of the pluses for a glass mount are:
- Inexpensive. My current is a Tram 1199 which is less than $20.
- No holes to drill or magnets to scratch paint on the vehicle.
- Good performance on 700-800 mHz and VHF/UHF. Great for air band and railroad. VHF low OK with strong signals.
- Low profile. And if still too tall for garage can easily be folded down.