UPDATE:
I received and installed the replacement light, and it all works just fine. I've been commuting with it for a week now and can report that the asymmetrical lens definitely provides a more expansive, brighter field of light from 0-50 feet than the symmetrical lens, but it does not do nearly as well beyond 50 feet. I can see why these are used together (with a dynamo that can support 2 headlights) to provide the best of both needs.

I think the asymmetrical is a better urban/commuting light (my present use) as it provides a really nice field of illiumination - broad, bright, and very uniform. My wife said that the tail light is quite bright (I had her watch me ride when I was testing the installation).

The capacitor keeps the headlight and tail light illuminated at a modest level at stoplights, and the light levels increase very quickly. I'd say the light achieves full brightness at 3-5 mph. I'm very happy with this setup.

System: Shimano Alfine Dunohub, Supernova E3 Pro Asymmetrical lens headlight, Supernova rack mount 3 LED tail light.