Not worth buying unless someone sell for you at cheap price, egpu are costly from scratch, even one with a RX580 can be sold for 530$+ where as a discrete RX580 don't cost up to that at all, I can still get a RX580 8gb at 370$
I'm guessing he or she got the cards earlier before this month, in January I still see price for one RX580 at 360$ on ebay but it doesn't take some time before the graphic card vanished from the website, only 4gb versions are very cheap right now
Where are you seeing RX580's 8gb for $370....$529 is lowest i find for a new 580-8......that is in stock and can ship...no point in ones not in stock.