I never buy physical boxes and I bought 1 box of Compendium and 1 box of Series 1 to use as trade bait for cards I wanted versus hoping they found their way off the ePack site. Overall, I found it enjoyable. I think it could be the way of the future and a huge pro, as was earlier mentioned, is seeing tons of cards and multiple copies out there for trade. It prevents people from just burying things and never taking the effort to sell them even though there might be a market out there.
I would like to see a cash trade option, similar to COMC, instead of only being able to trade for other cards. That might entice more people to use it and UD could probably bake in some service fees and earn a few extra bucks themselves.