Send your most visible exec out with total crap in his hands?
Depends on the exec. Some are completely incapable of doing this - they either panic and push the wrong buttons or fail to gracefully recover when they fumble.
When you are starting off, the goal is to demo the vision, not the product. So it is not only ok, but commonplace to have incomplete/buggy device. But if your execs cannot pull off these kinds of demos, the whole thing is DOA.
A failure will not appear until a unit has passed final inspection.