I've bought 4 guns from AIM Surplus in the past 2 months or so. Customer Service was very nice and helpful, delivery time was very good, and the guns were all packaged and wrapped well. Shipping was also reasonable.
2 of the 4 guns I got from them were Mosin Nagants (round receiver), and I got them just last week. I'm very happy with the condition they arrived in, though I would recommend against getting the hand pick option because when I asked the guy if they would check the bores for you, he said they only pick the ones with the best looking outer appearance without checking bore condition.
There isnt much difference between the round receivers and hex receivers other than the front ring being round vs hex shaped. They both fit in the same after market ATI stock. I think the hex receivers are usually alittle bit older and less common than the round receivers, but mostly its about the cosmetic cool factor in the hex receiver. If you think it looks cool then go for it, $10 isn't that much. I already have a hex receiver so thats why I went with the round receivers this time.
The other 2 guns I got from them were a beauitful VZ-24 and a Romanian PSL. The price I paid for the PSL including shipping and transfer fee was still less than 3 other places I found online that had PSL's.
I'll definitely be doing business with them in the future.