Through glass antenna really only work well for digital signals. That's why cell phones can use them. With a digital signal, you either receive it or you don't; there's no real signal degradation due to drop offs in signal strength. As signal strength deteriorates, you'll still read loud and clear until it drops below the point of receiving it, and then you drop off the air completely.
I've tried through-glass antennas before. If you only need to reach vehicles within line-of-sight AND your radio's electronics are stout enough to not burn up trying to broadcast with a bad SWR, then that type of antenna can be a simple, elegant, and aesthetically pleasing solution. But I wouldn't run one with a radio that didn't have an overheat protection circuit.
Also, a lot of modern radios can and do ground the antenna through the insulation jacket of the coax cable and then through the power supply. So if the radio itself is grounded (which it will be through the negative power wire), the antenna is grounded, and there's no need for a ground wire from the antenna base to the frame. The ground wire won't hurt, and can sometime improve SWR, but it's possible to get a decent tune without it.
That's electrical grounding, or continuity, of the antenna. It's not the same thing as ground plane. A ground plane is a flat metallic surface perpendicular to the antenna that the broadcast signal reflects off of. In the our case, the roof of the truck is an ideal ground plane, and it's why the magnetic mount antennas placed in the middle of the roof generally have the best SWR. NGP, or no-ground-plane antennas, are for mounting on the roofs of fiberglass bodied RV's, semi truck mirrors, etc. So NGP antennas are ideal for a lot of us that are mounting the antenna to the door jamb mount, the tire carriers, or hanging off the side of the roof racks where there's a good ground plane on one side of the antenna and nothing on the other side. I have an NGP Firestik on a Fourtreks mount on the roof rack tube, electrically grounded through the radio, with an SWR of 1.8:1 on channel 19. It tapers off a bit to around 2.1:1 on 1 and 40, but considering the mounting location, I'm really happy with that.
I've also found that a little Never-seez on the threads of your coax connections improves electrical continuity, and in my case, makes it much easier to remove the antenna for the car wash.