The simple circuit is missing "pre-emphasis" then it will sound muffled on a normal FM radio. All FM broadcast band transmitters use pre-emphasis to boost high audio frequencies then all FM radios use de-emphasis to cut the boosted highs back down to normal then any added hiss is reduced. The de-emphasis in an FM radio will also cut high audio frequencies from this simple transmitter.
Another problem with this simple circuit is that it is missing a voltage regulator. As the battery voltage drops then the radio frequency slowly changes.
Another problem is that the LC tuned circuit connects directly to the antenna so the frequency changes if something moves towards or away from the antenna.
I improved this circuit by adding pre-emphasis, adding a voltage regulator and adding a transistor between the LC tuned circuit and the antenna.