Hey Bill,
On the Xvos, I expect Chels will do what he's done in the past, which is wait until all planned units have been pre-ordered, then begin cranking them out. In that regard, the initial projections can sometimes be approximations. They may do these differently though, which is one of my points interest to watch.
They're usually good about keeping people updated though, so it may be a good idea to subscribe to their Supplier thread (assuming it's still live).
The Railbox. I liked it a lot. It was very cool technology, especially at the time. I used it for awhile then eventually sold it off. It's very big, and it was getting harder and harder to reach for it instead of one of my Xvos, which are tiny in comparison.
They (RBs) do require a small bit of maintenance to ensure that all the moving parts keep working smoothly. It's nothing crazy, but it is important that an owner does them, or the mod will eventually start giving you problems.
All in all, I'd say that's a really nice deal if someone was interested in trying them.