In college, I worked as a lab assistant for a professor studying them. I spent a lot of time counting microscopic young, scraping adults off of traps, measuring and weighing them before cracking them open to scoop out their insides and weighing them.

These little fellows are, in general, small. I guess they can get 50mm (2in), but most aren't that large and they have thin shells.

Further, I'd be somewhat afraid that creating products from them would spread the invasive species even further. The professor I worked for studied them because of their invasiveness - the lakes he set traps on were obviously spread by people. They spread easily by the water in boats - microscopic young means people don't know they spread them.

As noted in the article, plastic buttons displaced buttons made from clamshells long ago. I doubt a market for zebra mussel buttons could make any dent on the population.

An economic incentive to hunt a particular species does not result in a decrease in population. What you have instead is an economic incentive to breed large populations in uncontrolled conditions, likely on public land, which then get abandoned and/or released when you realize the economic incentive has made your invasive species problem far, far worse.

This has happened many times throughout history.

Probably not as economical as cheap plastic buttons, and harvesting them at low cost would likely disrupt native species too

you can use anything for buttons if you are dedicated enough and have the right tools