Nothing wrong with either mask. The MAG has tighter sight-lines due to those thick bars. I'm in a similar situation with the MAG and an Adidas. When I switch back to the Adidas for a while, I notice more open sight-lines due to the thinner bars and the "fuller" profile of it.
As for protection, both will get the job done. The issue with +POS and Adidas is that they are hollow steel and therefore will bend. It's not a matter of IF, it's WHEN they will bend. The positive is that they're cheap (normally under $50-60 each) - but they're getting harder to replace now at that price and the +POS is basically a dinosaur now since you can't get them from Dan Parsons (of Parsons Official Supplies aka pluspos.com) anymore.
Why do you think there are so few of these coming up for sale used? My thoughts are two-fold, they command much smaller size of the market in the first place and then it is my humble opinion that they get bent and discarded, so very few make it to a second-hand sale. I know this is true with the Adidas and +POS I have had personally.
I like them, but they bend and you just have to learn to expect it. Literally, the first game with a new Adidas last year and it bent. Varsity baseball and the kid wasn't throwing that hard, high inside pitch fouled back straight to my eye-port. The AS MAG LUCs did their job and I shook it off with no lasting effects, but between innings I took a closer look at my mask and noticed it had pushed the eye port back closer to my face. The profile was flatter than it had started, which was less than a full profile to start with, but still straight. I've worn it a few times since then, but not in another Varsity game. I can't take the chance of a weld failing/popping, so it's reserved for the 15U guys now.
YMMV... but based on what I hear and have read on here, that's the main problem with these hollow steel frames. The higher the level, the greater the risk of a bend.