Depends on where you live .. Hub Dynamo powered B&M 2LED Toplight Line Plus
is enough for me where I Live..

have had a 4D senso, now senso plus, on another bike for years..
2AA power the light , in senso mode , and shut off after 4min.

the line tech one is smaller and flatter but still it lights up the whole surface.
capacitor keeps the light on when stopped .