If you can get a Digit for $300 I'd go for it. You could probably use it for a couple of years and then resell it for more than that. The Extreme, at $155 on eBay will not be covered under warranty by Arizer. They're cracking down on resellers. Personally, I think that vape companies who allow their products to be sold by anyone and everyone for years, and then come out and say that only buyers from authorized resellers are covered, are not being ethical, but that's the way it is. That eBay seller is shoveling some shit too, claiming you get a lifetime warranty. That's only on the heating element.
"We now require an Authorization Number and receipt copy for warranty service. Sellers under MAP will be pointed out and noted that we don't honor the warranty on your discounted stock."