I own one, so I know they exist. 
But it doesn’t appear to be available anymore, and usually product numbers go up with new versions. Is the 380 newer than the 390? Why can’t you buy the 390 on the website anymore?
Yes, you’re right. The 390 is no longer available for sale. It was a great model and was superseded by the 580. 
The 580 has two more WAN ports, and we are offering it at the same price as the 390! The 580 is therefore another popular model now.