I sent an e-mail to Synology's info address and got a response a few hours later (not too bad). It wasn't terribly good English, but said they "quickly sell out" of the DS411+ and it should be back in stock in 1-2 weeks.

Amazon has 8 of them now, but NewEgg says it's "deactivated".

FWIW.

Cheers,
Scott.
(Who still isn't sure if that's the one to get, as it's probably vast overkill...)