You can get a reasonably priced mag mount with an NMO mount, and then just get the antenna separately that fits. I personally have this Browning that is great for the price. Note that you'll still have to tune it using the swr meter but that should just be a matter of trimming the whip until swr is in line.
I've had great luck with a Browning NMO antenna (450-470 Mhz) paired to an NMO trunk mount, but would likely work fine on a mag mount too. I can hit our local repeaters 20+ miles in heavy urban environments around Washington DC, granted the repeater is mounted extremely high up.
Browning 450MHz-470MHz UHF 3dBd Land Mobile NMO Antenna https://smile.amazon.com/dp/B00IDTJ2EA/ref=cm_sw_r_apan_glt_i_R2PG1ETETD6SCFAQHP5P
Browning 450MHz-470MHz UHF 3dBd Land Mobile NMO Antenna https://smile.amazon.com/dp/B00IDTJ2EA/ref=cm_sw_r_apan_glt_i_A16ABG6ADFBRSSVYN2M9
No kidding! Not sure what I was thinking when I ordered it. The frequency ranges listed on it dont seem to be appropriate for CB or GMRS, Im going to see if I can still return it. I went with one of these:
https://www.amazon.com/gp/product/B00IDTJ2EA/
Im hoping to be able to switch out my antenna & radio between CB / GMRS using the same cable and NMO mount (use GMRS when im out with the guys wheeling, keep the CB in there day to day) but CB will come later, for now I want to dial in the GMRS first.
I appreciate you putting this on my radar - I had understood that tuning your antenna could get you better reception, but I didnt realize that having your antenna not tuned could potential damage it. Ive looked up a few tutorials on tuning GMRS radios and will do some learning.
The squelch thing - I kinda get what youre saying there, I havent made use of the squelch yet, but it seems kinda goofy, I like how on the CB`s you can adjust the squelch with a knob, seems more intuitive.