Correct me if I'm wrong, but doesn't a bike generator put out AC? One would suppose that someone marketing a plug-in LED bulb must have provided the circuitry for rectification as well as a heat sink. Of course it all depends on the execution, doesn't it? Someone could have used a single inline diode, in which case you'd get a duty cycle of only 50% (like a PWM control of only 50%), which is to say not as bright as it could be. On the other hand, that's one way to control the heat if that's all the fitting can handle. And of course a tiny screw-in bulb is unlikely to have a supercap to provide a stand-light capability.

For what it's worth, the B&M lights are marvelous and do provide a stand-light feature. They are expensive (but my own scarce time to build the circuitry is worth more than that). If you want a C&V-looking light it might be simpler to mount a new B&M light in an old housing.