You might have noticed problems with that extremely simple FM transmitter:
1) Its radio frequency changes as the battery voltage runs down. It needs a voltage regulator.
20 Its radio frequency changes if something moves towards or away from the antenna. It needs an RF amplifier to isolate the tuned oscillator from the antenna.
3) The sounds heard on a normal FM radio are muffled with levels reduced for high audio frequencies. It needs pre-emphasis like all FM radio stations have.
You might have noticed that the "Engrish" on that website is awful and frequently wrong.