It seems to me the simplest explanation of BitUSD is something like this:BitUSD is a currency that is backed by a network reserve of at least two times the value in BTSX. The reserve is available to support a full monthly buy-back of units no longer demanded.
Much of the marketing material refers to two parties (e.g. Alice and Bob) coming to an agreement (like a derivative) where one takes the risk of BTSX and the other doesn't. This seems somewhat irrelevant to most potential BitUSD users, who may never need to deal with BTSX in any way, and although the principle is similar, is not really an accurate reflection of the mechanics, as there are no individual contracting parties.
To me, the simplified description also highlights an important feature of BitUSD over NuBits, in that shareholders do not hold adequate reserves to support buying back 100% of its NuBits.
[When the material presents BitUSD like a derivative, it becomes very confusing. I've been here for a while and have misunderstood how mechanisms like short-covering or margin calls affect BitUSD owners (they don't). Thanks to members like Troglodactyl and Chuckone pointing these errors out to me.]