I haven't tried calibre-web, but has been on my long todo list for a while. If I'm not mistaken, it is not a better UI, it is a better UI for a web server, calibre's web server is... Well, barebones. So it is meant to replace it when you want to access the library mostly remotely. That's what I have understood, maybe I'm wrong so take it with a pinch of salt. The other comment had a link to an alternative open source free software library manager, might be worth checking it.