I wonder if this is new or refurbished?
They’re refurbished. It’s stated under the price on the sale page. 
They refurbish them well! The ones I got looked brand new. My kids loved them, and hooking them up to their Freetime/Kids+ account was easy.
Are these pre-ad-free or will I need to purchase the account upgrade myself? Not a deal-breaker tbh but since it doesn’t specify as with the 2018 model, it was a question I wanted to ask.
From the Specs page,
Reader (Includes Special Offers)
So I would assume that these are ad-supported.
All the Kindle/fire devices from Woot that I’ve seen are ad enabled. I got one of these - “good” condition but seems excellent, btw - and figured I’d spring for the ad removal ($25). But they’ve been so unobtrusive that I haven’t yet bothered.
I love mine. For $20, this is a steal. Also got the $5 leather case they linked. Not trying to pay a hundred or so for an e-ink display.
Since these are circa 2015 I wonder what the battery life is… Are they “original” from 2015 or do they replace them during the “refrub” process???
The battery is tested as part of the refurbishing processes.