And with the Superflash, you can't easily see if one has fallen apart while underway.
Never had a PBSF fall apart in over two years of use. Battery life with the Cateye is not great, so that several times by the end of a commute, when I thought I had a taillight, it was actually out. So even if I was using a Cateye, I would install two since I want the redundancy for a critical piece of safety equipment. My main concern is visibility, and the PBSF is the best for the money.