A friend of mine designed a bike related product that he 3d prints and assembles at home. He’s sold 1000+, it’s quite niche and sells for £50-£150 depending on version. It’s constantly evolved over time and is even being used by pro road teams now.
It’s potentially patentable, but really wasn’t worth doing without the money to enforce. He’s quite up on the patent process and holds a couple obtained through his day job.
He’s even open-sourced the models for the 3d printed parts so people could make their own or print replacement bits – there’s a net positive of this as people see the approach, think “that’s good”, but 99.5% of people will just buy the thing.
As with the mudhugger/crud catcher, brand and reputation count for a lot.