Fenderbot is ok. Designed more for long run times than brightness. So there is a compromise, but some have complained about the pricing to performance when compared to the Radbots. Not many fender mount light choices even for fender mount reflectors.
OT; I found/put on Zefal rear lights that fit on my seat stays as well as the rear rack (PD Radbot 1000) for max coverage and insurance if one light happens to run out of power.
Might buy a Philips Saferide rear light to get more side coverage due to the lighted ring design of the lens. Then I can move the Radbot to a higher position, either the seatpost or helmet.