I’ve ordered from them quite a few times over the years. Some orders shipped fast, but some orders took a long time to ship. They are legit, but I wouldn’t count on fast shipping
They're OEM Glock mags. I have bought packs of 10 mags and several 5 packs back when they ran specials on them.
If the prices are good, have no worries buying from them.
I've heard of trouble with their customer service years ago. I did take a chance and purchased a firearm from them back in 2013 or 14 and it arrived as described. No need to deal with customer service.