Pi-FM-RDS, from which this project is forked, warns under its Warning and Disclaimer section that "In most countries, transmitting radio waves without a state-issued licence specific to the transmission modalities (frequency, power, bandwidth, etc.) is illegal. Therefore, always connect a shielded transmission line from the RaspberryPi directly to a radio receiver, so as not to emit radio waves. Never use an antenna." They literally warn users not to do what this project tells them to do. I can't be arsed to do the proper math but a casual check suggests that the output power from the Pi could easily exceed the FCCs low power FM transmitter exemption.

The project also cursorily mentions the need to use a bandpass filter to avoid interference but fails to explain the specific device needed or how to wire it up in the instructions.

[EDIT] I debated whether or not to say it but I will: this is just irresponsible. There is no way to legally use this project as is. The user would have to have additional knowledge of RF hardware and regulations to make it compliant.