The Microtech Gefell DM 622's are vintage small diaphragm dynamic microphones that are somewhat rare and unknown. I only had the chance to try these out recently when I was an assistant engineer on a session where the engineer brought them in to use. I was surprised to find that they were dynamic mics, as Gefell (an offshoot of Neumann), as usually they only will make condenser microphones and I'm not sure that I've ever used a dynamic from Gefell and Neumann has literally only one and they just made it within the last few years. These are also omnidirectional mics.
The Microtech Gefell DM 622 are pretty cool microphones to use in some unique situations. I don't think too many engineers will be coming across these any time soon as they seem to be very rare and not too many people know much about them. I had never heard of them until I had the chance to try them out, as they're actually really cool sounding. The engineer was using them as room mics, which I thought was an interesting until I heard it and they sounded great! They pick up a good amount of detail for a dynamic microphone and I could see how they would be mistaken for condenser mics. They're good as room mics since they're omnidirectional and will pick up everything around them. I'd be curious to try them out for some applications as I'm not sure what else they'd be good for as it's definitely unique to have a mic that is both dynamic and omnidirectional. I haven't seen Microtech Gefell DM 622's for sale at all, so I'm not sure what they would go for if you could find them. If you're into vintage mics, the DM 622's might be pretty cool to mess with since they're very unique.