Its a good start. I like the extension but not so much to give 5 stars just yet. But still great work. To suggestions Mordynak wrote I'd add few below:
1) Customizing the containers as you'd like. At the moment there are only 5 categories. I'd like to modify or remove some them completely and replaced with my own.
2) Possibility to hide tabs in containers from the browser's tab bar. Possibility to show only these which are inside of focused container.

Cheers