It's both. Not great for suddenly offline, as you need it on all the time and it is slow. But if you can plan it like, you're going in a mine, or spaceship or airplane, or the bush, or an alien attack or whatever... and you need offline to keep reading, then this works.

You can have archives from x day or x week or whatever, organized yourself, versioned with git, as you like, to save web content through version changes, removal or vanishing.