Review on HiLetgo RDM6300 125kHz EM4100 RFID Card Read Module with UART Serial Output for Arduino by Joel Norfork

Connected and started fairly quickly. I found several libraries on the internet. There was no RFID tag in the kit and the first ones I bought are not compatible. Apparently 125kHz is not enough, it needs to be compatible with the EM4100. It worked when I had the right tag. The only other RFID reader I've used and compared to is the RC522. Their sensitivity seemed about the same at a distance of about an inch. With one library I tried to output the value continuously while the tag was in scope and with the other it didn't. The RC522 was only ever issuing one read per day. The RC522 has the sensor coil built into the PCB, but this is in a separate coil. Which is better depends on how you want to integrate it into your project.