I don't know for sure, but probably that's sufficient. Usually, USER_NS is checked for when installing on Gentoo. So, that's a hope. Main advantage is getting access to Qt 5.12 and later to Qt 5.14. Qt 5.12 WebEngine corresponds to Chrome 75 (June 2019) with additional security patches applied. As for browser, its less feature rich than the stock one, but we are working on it with Plasma developers.