They don't have everything all of the time. But they DO have ammo in stock from time to time. Their prices are GENERALLY pre-hysteria. They are a very reputable company. Customer service has been a little spotty at times, but they have been overwhelmed with orders for months. Their lag in shipping has dropped from 15 business days to 5 in the last week or two.
As far as AR parts, they make most of their own, and have a really good rep for making quality parts and fully assembled guns.
I have built an AR from parts that I bought almost exclusively from them. It went together easily and TIGHT.
As you can guess, I highly recommend them.