I’d agree with Vik that the Radbot is bulkier than the superflash which makes it a bit of a pain to mount. You can also find plenty of evidence on the web that the Radbot is much brighter.
I was curious about runtimes. Portland Design Works claims a 15 hour runtime on steady whereas Planet Bikes says about 100 hours (presumably on flash mode).
Here is a time lapse video of the two lights.
The lights started running at 8 pm, the video starts at 9:30, one frame per about 6 minutes, and the Radbot cuts out between 1:19 and 1:25 am, i.e. about 5.5 hours runtime. The superflash was dim but still lit after 12 hours. Both lights were running freshly charged Duracell AAA rechargeables, specifically the low discharge precharged versions with white tops are that allegedly the same as eneloops. The video is only about six hours long because I’m still figuring out the quirks in CHDK.
Conclusion? The runtime on the Radbot is somewhat shorter than advertised. This is certainly consistent with my experience using it on flash mode on my commuter. Every couple of weeks, it goes into a low battery mode where it turns off, and then when I turn it back on, it will stay lit for something around 5 minutes before dying again. In comparison I don;t have to recharge the superflash more than a couple of times a year.
There is also a question as to how bright a taillight is useful. I would go mad if I was following either taillight on flashmode, and the PDW is almost blindingly bright on steady. I know that randonneurs prefer to run their lights on steady mode, and I’d be interested to know if their runtime experiences with either light are consistent with what I’ve found.
Jim raises a good question about reproducibility in the comments thread, so I reran the test with both lights using a different set of batteries: Sanyo Eneloops. Although the time lapse failed, by intermittent observation, I saw that the Radbot cut out between 5 and 6 hours, and the superflash lasted more than 12 hours, so the results were qualitatively the same as before.
Kent Peterson ran a battery life test of the RADBOT 1000 versus the new Planet Bike Superflash Turbo (1W). He got about 6 hours of life on steady mode for either light, which is in line with what I measured. Bottom line: if you need light on steady mode overnight, use the 0.5W superflash, which is good for 12 hours.