"I suppose I am a purist and have yet to ever purchase wine in a box"
A purist ... so, buying your wine in open top amphorae covered with a layer of oil to keep it fresh? Yeah, things just aren't like they used to be.
I have heard/read good things about "boxed wine" recently, but I must confess I have only tasted a couple of examples (which ones they were I do not recall). What I do recall is that they were ordinary (shall we say pedestrian), drinkable wines.
Among my problems with this format - boxes - is that the size of the packaging makes them seem less inexpensive than they are. The boxes often contain 3-5 liters. When I am purposefully seeking an inexpensive wine, I'm looking to walk away after having broken a 10-spot and received some change.
The problem is when six $5 bottles of wine are packed into one 5-liter box it costs $30. When I'm buying cheap wine, I don't want to spend $20-30 on one "package" of wine, be it a bladder in a box or a gallon jug of Elmo Pio (actually, to be fair to Elmo Pio, whose son attended school with my father, I'm pretty sure his wines sell for far less than $30 a gallon)