Why do you want to buy a Radio Aid when you have hearing aids, cochlear implant, bone attached hearing aid (BAHA)? The main reason is the capability of the microphone in your hearing instrument allowing you to hear clearly over distance. Other factors can include the type of hearing loss and the severity of hearing loss.
Before I go any further - Radio Aids are also known as FM Radio Aids, Digital Wireless Radio Aids and Wireless Communication Products. Also Hearing instrument being the term used to cover hearing aids, cochlear implants and bone attached hearing aids. I'll have to change this as time goes when another terminology is created!!
In their simplest format a Radio Aid consists of a transmitting microphone and a receiver that works in conjunction with your hearing instrument.