I tried to use this at the weekend - with no luck. Now in fairness i live in central london - and theres not much in the way of free channels. I also had no luck with a simialar stand alone fm transmitter. Part of the problem being my cars tuner only having auto scan - whcih shows station names not frequencies - so its hard to know whats free.
So i ended up randomly trying frequencys with no luck at all.
Your mileage may vary.
UPDATE - outside london it works much better. I also tried an external module - with similar results. Seems London’s wavelengths are saturated.