Glad to see this. Show HN has always been my favorite part of Hacker News. Anything that can inspire more creation and help product builders find an audience, is a good thing, imo.
I only recently joined Product Hunt, but to me the major differentiator is that Show HN are self-submitted products, while Product Hunt is a curated list. That means I'm more likely to find higher quality and interesting products on Product Hunt, but I'll be the first to learn about a new product from Show HN.