I have tried to generate some interest in SSFs on the XDEV board, on several occasions, since my first post (last May). There was a brief flurry of discussion a couple of months ago, but it soon faded out. It has always seemed to me that XDEV and SSFs provided a very good fit, conceptually. I really hoped that the profit possibilities of using SSFs would intrigue Myst so much that it would/could justify an XDEV version tailored to their use. I seem to have this (annoying to some) habit of being right to early. Actually it's a blessing and a curse.
I am very interested in SSFs, and have done a significant amount of research in to them. They are definitely a double edged sword, due to the leverage.
And, yes they do expire, like all futures contracts. They trade on several calendar months.
Here are a couple of links to help bring you up to speed.