I use a bottle generator with one of the cheaper B&M halogen sets. Since it came stock with the bike, I'm not sure which set gets specced... but given the pricepoint, there's no way it's a top of the line one. It is a good light for seeing with on a road, but it would not be bright enough for off road use. Potholes don't get completely illuminated, and if you're going more than about 15mph you are at risk of outrunning the light on bad terrain. (since it's trivial to bust 35mph on a bike going downhill...) There is a standlight feature, and it runs for at least a 2-3 minutes when the generator isn't receiving power.

The generator I have is fairly good, but it will fail in wet conditions. Water will cut friction enough that it can't generate light anymore. Since one of the reason I wanted a generator light system was for riding in the rain, this is irritating. I'll eventually need to upgrade the front wheel to a hub generator to eliminate this problem.

Bottle generators also chew on your tire. Not a *lot*, but I do expect the rear tire to wear out sooner than it might otherwise. And it means I don't run lights all the time, even tho I think it'd be a good idea.

Lastly, a bottle generator makes it a bit harder to pedal. It usually feels about one cog higher than it really is.