Busch & Müller SecuZED Plus Dyno Tail Light for Fender, Frame or Seat Post
B&M SecuZED Plus Dynamo Rear Light for Fender, seat post or Frame
This one is just as good, maybe slightly better, than a Secula - just get whichever one is in stock, they're both way past the "good enough" threshold. All dynamo lights these days, even the cheap ones, are more than good enough.
This one mounts to the seatpost, seatstay or fender.
The stand light capacitor fully charges within about 3 minutes and will stay on for at least 15 minutes. It stays on long enough.
There's overvoltage protection to keep the electronics from getting fried and the connections are non polarized which makes installation easier.
Made in Germany. StVZO (fancy German road regulations) approved.
If you want a good sized dynamo taillight that mounts to your seatpost or seatstay, get this one.
The wire to power it from the headlight IS included, yay.