Honestly, if your willing to learn to use LibreOffice, it's way more powerful than OnlyOffice. It took me a minute to get used to it too, but once you do, it's pretty awesome. And if your worried about UI, you can change some of those things in the settings, like you can make it have a MS-style ribbon at the top. If I were you, I'd spend two weeks trying LO, I think you'll get used to it pretty quick