What’s the difference between buying a used TX or a couple used RX? Unfortunately we don’t know exactly what the OP has which makes it rather difficult to offer advise. One thing is certain and that is Airtronics/Sanwa no longer manufactures aircraft radios. 90% of the time when it comes to advising a beginner or someone returning to the hobby I suggest going with Spektrum gear. They currently have the higher market share and if the OP has a club near by he will be able to find assistance. The 2.4 Airtronics gear was only popular with the sailplane guys.