Some people do buy a used radio for a buddy box,lots of clubs have buddy boxes and instructors but as MinnFlyer stated,if you buy a radio or radio/buddy box and very few people at the field have that brand ,may find yourself waiting for those few to show at the field while other people are flying,that has happened at two of the clubs I fly at. My advice,better to be safe thah sorry, check at the field before spending your pay check,but again I do have a bridge trying to sell?