EDIT: looks like this is covered under "Reserve Deficit Sell Penalty". I don't really understand this part but regardless this won't be pegged to the dollar.
Then, a month from now, if you want to sell Unum and get ETH, maybe the price of ETH is $500. So you send in your 400 Unum, and get .8 ETH.
In other words, you send in $400 of ETH for 400 Unum, and if the price of ETH goes down to $300 and they try to cash out all 400 Unum...?
You might equally say "isn't it possible that Tether could just print Tethers out of thin air"? And the answer would be "yes", but people still find utility in it.
So basically Unum is trading "risk of value going down/up" for "risk of smart contract bank run"?
EDIT: Also, I'm really interested since this is the first smart contract use case that I've managed to understand. Which is good since I'm all-in on ETH :)
EDIT 2, for anyone reading this thread: here's the announcement thread, answers all the questions I had here: https://bitcointalk.org/index.php?topic=2473877.0
Compared to holding USDT, the tradeoff is that Tether can't print themselves free USDT's, but you have a risk of a smart contract bank run.
How will you have the reserves to pay out everyone who wishes to cash out all of their Unum 1 month later if the price of ETH as dropped by 50%? Where will you have the funds to do so?
Edit: I see from your website you have a penalty in place for when your reserves drop below Unums in circulation - clever play! (https://unum.one/#!/learn#reserve-deficit-sell-penalty)
You're right that relatively few people have the technical skills to query a smart contract, but that relative few is still a LOT of people who can verify the reserves independently. Versus the almost 0 people who can audit Tether.
If you're interested in interacting with the smart contract (or any smart contract), you may want to install Mist. It's non-trivial to get started, I admit, and the tooling around smart contract is incredibly immature, but..man it's cool ;)
https://github.com/ethereum/mist/releases