The current state of Isle of Man brush making hearkens back to the 1960s when Gibson and Epiphone guitars were built side by side by the same craftspeople using the same techniques and materials. While the guitars had obvious differences (to guitarists), they were and still to this day remain fraternal twins.
I’ve owned two other Vulfix brushes. Like these, quality was top notch. Really, the only significant differences I can point to (beyond the decal) are the naming of the hair grades and density of the knots. In my experience, Simpson branded brushes are typically denser than Vulfix. Simpson Best badger is equivalent to Vulfix Super badger. Both brands offer beautiful and unique handles. And regardless of the badge, when you find a knot you like, it’s lightning in a bottle!