Based on the community feedback, the main practical difference is the filter ring material and how it behaves in use. B+W XS-Pro filters use brass rings, while Hoya filters are commonly described here as aluminum. Brass is generally less prone to sticking or binding in lens threads, especially with temperature changes or when stacking filters. Several users specifically report that Hoya filters can bind more easily, while B+W filters are easier to remove.

The answers also note that B+W uses Schott glass and that many XS-Pro filters include MRC coating, with some versions adding Nano coating. However, from the provided answers there’s no clear evidence that image quality is dramatically better on one versus the other in normal use.

So, if you care most about handling, durability, and reducing the chance of stuck filters, the extra money for B+W XS-Pro may be worthwhile. If your priority is simply getting a good filter at lower cost, the answers don’t prove a major optical advantage over Hoya HD.