Thanks for your question. You should be able to open it, but Lite removes most of the controls (randomly) so it's not that useful. This is an unfortunate result of Apple's policies on Lite apps (we cannot offer a timed demo version, for instance) and the way that Lite is structured (i.e., our fault).
That said, if you ask any questions about the X3 layout to its creator, he'll be glad to respond (I think), and perhaps even make a video of it in use (hopefully).
Thanks for your question and thanks for checking out MIDI Designer.
P.S. If you cannot open it meaning that it crashes or MD does some other strange behavior, please comment back here and we'll investigate.