I compared it with this online SDR radio http://websdr.ewi.utwente.nl:8901/
and I seem to be able to receive more radio stations per band.
I presume then that the sensitivity is in the microvolt range if not at the sub-micro volt range. People experienced with regenerative receivers will notice that you can tune within a few 10's of Hz of even a strong AM carrier before you get frequency lock. You can also hear the effects of a very narrow bandwidth on the audio quality. Further evidence of the narrow bandwidth is the seashell sound effect you can get tuning across an AM station.
The lack of frequency lock makes it a good choice of circuit for SSB reception. The circuit also has very low frequency drift.
I used permeability tuning in the radio with ferrite material. If you used a variable capacitor there would be less need to adjust the regeneration controls.
With the SDR you don't hear the effects of phase noise. With the regenerative receiver when you are listening to weak to intermediate strength signals you can hear the background noise increase and decrease as the signal increases and decreases. This is due to phase noise to amplitude modulated noise conversion acting on the carrier. I suppose it is fortunate that the conversion is proportional to signal strength. Of course when you set the regenerative receiver to the just oscillating state you will hear a constant amount of background noise as the oscillation is converted to AM noise.