Everywhere you are
Web
NewTwos runs in any modern browser with nothing to install.
What it is good at
Keyboard work. The web app has the full shortcut set, which makes it the fastest surface for anything involving a lot of writing or reorganising. See all keyboard shortcuts.
Wide screens. Sidebar, list tabs and a right-hand panel. See on a big screen.
Being available anywhere, including machines you cannot install software on.
What needs extra permission
Notifications must be granted per browser, in Settings Notifications Browser notifications. A browser that is closed cannot notify you.
Photo upload needs a working connection to the storage service, which some restricted networks block.
Web or the desktop app?
The desktop app is the same product with three additions: a global capture hotkey that works over other applications, a menu bar presence, and start-on-login. If you work on one machine all day, those are worth having. See desktop.
Going further
Offline works for what you have opened. Lists you have visited are cached and readable, and writing is queued. See writing when you are offline.
The Chrome extension is separate, for saving pages as you browse. See Chrome extension.