My experience with that is kind of the opposite. I'm using hub-generators with Edelux lights. If adjusted properly, they work great out on the open road in the middle of nowhere, either on a skewer mount or over the wheel. But, they're not necessarily that bright, and in the city, riding with a lot of car headlights and streetlights, the light tends to get washed out with the ambient, and makes it hard to see potholes, etc.
One other factor- I interpret "adjusted properly" to mean lighting up the road from about 8-10' in front of the bike on out to infinity. I have seen people point them down at the ground where you get a bright little rectangle of light right in front of the bike and can't see anything in front of that. And coincidentally, the riders I've seen that did that felt the need to use a second headlight as well.
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"be careful this rando stuff is addictive and dan's the 'pusher'."