I've been using various sizes of these deck boxes since Burger Tokens introduced them. I've used them for Magic cube packs, MTG Jumpstart packs, and Summoner War 2E faction decks, among other things. For Summoner Wars, the 30 Sleeved size is perfect. I use Arcane Tinman clear board game sleeves, and the decks fit very snugly with no wasted space.
I have no complaints about these deckboxes. They're sturdier than you'd expect for a plastic box, and I've transported them in containers and on their own without issue. They work best when full, as leftover space provides more opportunity for the box to be bent or damaged somehow. The flaps close securely and don't open up again without effort. Finally, at $1.20 each (at the time of this review), they're an excellent bargain.