These devices are illegal to install and operate. Only a licensee is authorized by the FCC to install these devices. The fact that they are easily purchased does not make them legal to use.
They are frequently the source of interference to commercial wireless systems and more importantly, they are frequently the source of interference to Public Safety radio systems.
There have been recent instances of law enforcement showing up at a location where one of these devices is in use and demanding it be disabled to stop interference to their radio system.