Here's the last card from 2012 spx that I just added to my collection today. These shadow slot cards, while an interesting addition to the 2012 lineup I felt kind of ran flat. I don't like the idea of accumulating all of these "half cards" in the chase to try to get the outer shell that you can put these in. These cards are super prevalent falling at about 2-3 cards per box. The outer slot cards are very rare. This idea might be good for those that break cases of the product but not so good for the box breakers. I think the idea would have been better if you were guaranteed one slot card per box, then it would not be so bad having 2-3 of these inner cards because you might have a chance to get the outer card. Then again, any of these cards are pretty easy to get on eBay so if you want the outer card just go shopping on the internet! I suppose the idea here was to get a bit of interactivity with some of the cards, people like to customize things so UD figured why not incorporate that into a card set? Personally I'd rather just have a single card that doesn't pull out, doesn't require a bunch of handling and stays mint in the holder, but maybe that's just me.
As a side note I've decided to change my focus on breaking boxes. I think the thrill factor of seeing what you get in a box along with the chance of getting cool 1/1's is probably better than searching for the best copy of a no-name 70's player. I enjoy modern cards more than I do vintage so I think for me, this is the way to go.