You are right in saying that we are taking on Gumroad. IIRC, most of Gumroad's traction has been organic/word-of-mouth, with little/no money spent on paid advertising.
We're still figuring out the best way to acquire users at scale by experimenting with both conventional (Reddit/Twitter ads) and unconventional (Discord channel/niche forum advertising) methods.
PS: Great suggestion! I'll be setting up & linking an example storefront on the homepage shortly.