Keeping your data in some app, site, or browser extension is a terrible idea. Once they go out of business, or their software stops working, or becomes obsolete, your data is gone. All the time you spent clicking, typing, staring at the screen - is wasted - and you can no longer use it for anything. If you choose a software which lets you export your data anytime in a standard format, you're safe.
uBlacklist browser extension - stopped working when Google slightly changed the format of their search results page
Panoramio - Google let users export their data, but it's pretty useless now without the app
Notion.so - tech nerds are obsessing over this amazing easy to use writing app. They kept promising an API (a way to export the content) for years, but it looks now more like it will never come. The site still works fine, but it doesn't let you use your content outside of their site. So, you can't put your writing there onto your blog/website. GitBook is the alternative. It hasalmostas good user interface (in some ways it's better). But, it lets you store your content on your own Github account, which allows you to use it anywhere.