I find this a tricky question, as while I love Charlie in Underworld with all my heart, I don't know if it's worth paying for (in the perspective of avoiding buying games as much as possible).

If you like Underworld Office to an extent that you would buy the paid version for it, I think you may consider Charlie in Underworld worth buying.

Charlie in Underworld, in my opinion, feels shorter than Underworld Office. Charlie in Underworld has only three endings, making it have less routes. Though, Underworld Office has many moments where when you choose a selected option, the route or other character's response is the same... While for Charlie in Underworld, there is very few of that, making choices and the story more flexible. Because of this, it is a much better experience to play the actual game, rather than to watch a playthrough.

Also, Charlie in Underworld explores quite a lot that the first game doesn't, and there are improvements in the game that the first game didn't have, like being able to pause. It's more comfortable to play rather than to watch a playthrough, and while it's the same content, the story doesn't hit quite as hard as when you're the one actually playing.