Most stuff plugs into the trainer port to use the stick data and transmits the stick positions to a different reciever on the approved list which is pretty long. Decency if you really like your old transmitter
Got one for my FP2r6 which is 60 years old. Multi format input and output, only issue is plugging into trainer port of really old equipment. You don't gain anything that the old transmitter didn't have for features, like elevons without a vector director© or electronic mixer , but in my case, I have custom sticks and springs giving me a super feel that no one but me likes. and I found that I can buy antennas for it still. Not an issue on the adapter.
cost wise, the adapter is about the same price as one of the cheapo new systems which does have all the bells and whistles, displays and functions and is already approved for GHZ band