The idea is good, having a UI framework that creates a single app that is usable on Desktop and Mobile, BUT they are ugly, there's almost no consitency and for some reason they look like they where created in the 90s. Also they don't really fit into the current KDE desktop, specifically the UX is also not great, e.g. the Discover App is awful, when you navigate through the menu you often don't know where you are or how to get a level up etc

Kirigami could really needs some attention from designers

Agreed. The kirigami framework needs a rework in the visual space.