What issues have you had? Mine connects fine without issue and the quality is ok at best but my car speakers aren’t exactly preem. My antenna is even broken off and has a hard time catching regular stations but no issues with my transmitter nor with the bluetooth part of it.

I have one that is bluetooth to cassette. Unfortunately, it has a lot of artifacts during playback. Opted for a bluetooth transmitter that connects to an empty radio channel? Frequency? Works well.

Do you have a threat model? It’s a good layout of what you deem essential in terms of privacy and what you are willing to compromise. Better than going down the rabbit hole of privacy.