It masks some woocommerce inputs on the admin side. For the moment, only the price.
It works only for prices, for now
Woocommerce only accepts numbers and dots as characters for price inputs, even if you have set you want commas or other characters. And that is how woocommerce says you typed wrong. Painting it red. But don't worry about it. This plugin accepts these characters the way you want. I'll try to override this Woocommerce's feature someday