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No dynamo on this.
I thought about it, and it's nice. But I'm not doing so many days of contiguous riding without the ability to encounter power. The rear lights with AAA batteries is universal and easy to carry spares. The front lights I have multiple battery packs for and can carry about 24hr of high beam lighting or low hundreds of hours of low beam lighting.
I just don't have the need for a dynamo. I'm not an ultra endurance rider or a multi-week remote area tourer.
I have two for a few reasons.
Given that these lights are extremely cheap, quite bright, take standard AAA batteries, and only look large in profile (they're vertically mounted and fit within the front profile of the seat post)... it's just a no-brainer to run two.
I may overthink this stuff... but it's dirt cheap, weighs nothing, and I feel it is a better thing than having a single nicer (read: more expensive) rear light.