Just as a follow up, for anyone interested, these ARE in fact essentially the same light in a slightly different package.
The functionality is the same, the brightness the same, the lens for the superbright LED on top is the same. The Sette actually has two blink/flash patterns plus a solid on, and the PB has one flash pattern and a solid on.
The batteries were already in the PB when I got it, so I didn't open it to inpsect the insides. But I did open the three Sette's that I got. The silicone gasket comes out of place easily and requires a bit of care to make sure it's installed correctly, but besides that these lights are a good deal. The mounting clip is better on the PBSF, but not $10 better.
We'll see what kind of longevity comparison there is. I put the PB on my bike, the others will go on the kids' and wife's bikes. I ride a lot more than they do, and on busier roads, so the PB will get much more use.