In reply to fire_munki:
The Tau is very good, though I only have the rear light: bright enough, good battery life, easily charged up, common sense low battery indicator, has never complained despite long rides in all-day rain and daily use through winter. The rubber bands to hold the thing on are a little scary at first but have proven durable enough (18 months of daily use). The band I have on the light won't allow it to mount on a seat post, only on the stays, but that's fine for me as I already have a seat post light. Not sure about mounting on aero seat posts, might be worth an email to Alpkit to ask.
I've had another one of alpkit's bike lights in the past and it was utterly terrible, almost dangerous if relied on to see, but the Tau is great. I returned the other one for a full refund so their excellent customer service sorted that one out.
Post edited at 07:59