I had bought a pair of Hustler MRMBNC mag mount mobile scanner antennas months ago for my scanners, but since I was moving soon I never did anything with them. Well, I unpacked them the other day and decided to try hooking them up to my Antenna Analyzer today and see what turned up.
They actually did quite amazingly well on GMRS, especially on the repeater transmit frequencies. My SWR readings were in a tight range of 1.06:1 to 1.09:1 and this was without any tuning. The results were a very pleasant surprise because I thought they would have been in the barely acceptable range and would need some serious tuning, but evidently I don't need to do a thing.
For those who don't want a permanent install (like me) this may be a very viable and cost effective option. When I bought these, it was a pair in one auction which I won for around $18.00 +5.50 shipping. I see they are going for about $22 each on various sites around the internet, and the ones on ebay are sky-high at the moment. You will probably need an adapter from a BNC connector to whatever type connector is on your radio.
I have a Radio Shack scanner antenna around here somewhere and will have to check that one out next when I find it.