I use this antenna on my Retevis HAM radio, on a magnet mount. Great SWR across both bands, including GMRS frequencies. Here's the odd thing. When I plugged my Midland GMRS xcvr into this antenna, the SWR was atrocious! However, the Midland was just fine with the little unity gain antenna that came with it. As I now need to replace that antenna, I'm a bit flummoxed as to what was really going on - why was the Midland's SWR so bad with the Diamond? Makes me think the Midland radio isn't really 50 ohms - and neither is the Midland antenna, so they play well together but not with someone else's antenna. *shrug* I dunno!
Hence why I included a link to the antenna analyzer, the analyzer will help you tune the impedance of an antenna before you attach it to a radio. If the radio has an actual 50-ohm impedance the resultant SWR will match the stand-alone antenna SWR. If not, the SWR should be close and easy to tweak the rest of the way to match the radio.