Fits 2 sleeved decks and has a compartment on the bottom for tokens/dice/etc.
It isn't "one box per deck" but for going to a tourney it's the only box you'll need to carry
For important decks, most people I know use the Ultra Pro Satin Tower.
https://www.amazon.com/Ultra-Pro-Black-Satin-Tower/dp/B00FRIE76I