There's a lot of Shure 444's and 526 looking mics out there at cheap prices, often rebranded with commercial radio company names, sometimes Shure itself that are not compatible with CB's expecting dynamic mics. The bulk of what's out there has controlled reluctance cartridges inside that are meant for radios that supply a mic bias on the mic line and also expect inputs that were compatible with carbon button elements that they were originally designed to replace. Most of those mikes have a split key bar for momentary monitoring the channel by disabling the tone squelch. The other lot out there that may not be appropriate were those that were used in paging applications. Often those only have a single, make/break contact for the mic element and not a spdt set for ptt/audio electronic switching.
+2's can be equally confusing. Easiest way is to look for the "shark fin" that the Japanese knockoffs didn't have. Then look for the gain control on the back. Most of these mics were set up for high impedance applications and you need one that's low Z. Some are switchable and the matching is via the amplifier and not a transformer. There's also battery issues with earlier ones that took a battery that's near impossible to get. The latter ones took a 9V battery. Some paging version also have the gain control and have a lift switch. The non amplified ones you also need to know what you're buying. They were made in crystal, ceramic, and dynamic elements. Also another problem is these mikes are pretty much 35-40 years old or more based on their harmonica microphone. There's an internal rubber gasket that's part of the mounting that may have gotten hard or crumbling. It serves to isolate the element from the mic and surface.
Best mic for all applications was the Super Side Kick. For some reason, most anyone I ever did work for eventually gave up the original branded power mic, and wanted a super side kick wired up. While there are variants, most all are switchable for relay and electronic switching and can be set up for high or low impedance. Private label versions and paging version may not. I don't think I ever seen one with a spit bar for commercial although the paging versions often have multiple zone switches. The Shures are good mics, but they're rather rare as dedicated ham or cb microphones and the bulk of them were commercial rebrands. Shure would make any kind of mic and in any type of impedance custom for big OEM's
