It is a simple circuit with poor performance:
1) It does not have a voltage regulator so its frequency will change as the battery voltage runs down.
2) It does not have pre-emphasis (treble boost) like all FM radio stations have so it will sound muffled on an FM radio like your stereo with its treble tone control turned all the way down.
3) It is mono, not stereo.
With a 9V supply, its output power is about 12mW.
Increasing the battery voltage to 13.2V might cause Q3 to overheat and the output power and range will increase a little.