I don't know anything about the mags, but I've ordered from Outdoor Marksman several times and never had a problem. A 5 pack of these mags is $59.95 and shipping to me in AZ is 12.29. That shipping cost strikes me as a bit high for 5 aluminum mags, but who's shipping isn't too high?
Edited to add: Shipping for one is $11.75 and shipping for 10 is $12.80, so obviously they have a minimum shipping charge, so it makes more sense to wait until you've got a decent sized order.