There were a lot of flashing taillights at PBP'19 unfortunately, there's just not enough people to enforce that rule with 6000 riders on the road... it was kind of annoying. You can get 38 hours of run-time on a rear
Busch & Müller Toplight, and some of their front battery lights get 5-10 hours depending on the settings. I use a B&M eyro as a backup front headlight and a battery secula as a backup taillight. I do like my dynamo lights since they are much brighter than the battery ones, but if you only have one dynamo hub there's a good case to be made for just running the front light off it if you ever want to move it between bikes it's a lot easier.