Hurry! The windowed ones are also available now and then for $17.99! These guys are on Ususal Suspects so I trust them. http://www.greygrouptraining.biz/category_s/116.htm
Wish Magpul would make them for DPMS/KAC AR 10/SR25 weapons, but They have told me that they have no plans to do so.
I ordered the window ones, not sure why as older mags seem to work fine without them but what the heck it's a novelty I guess. I ordered 10 and some MagPuls and I'll give some to the SIL for X-Mas.