probably a matter of taste, but IMHO it's much more sensible for the split plugin to work tab-wise instead of splitting all tabs
Can you explain what you mean better?
Probably "split document" instead of "split window". That is, the documents in which you choose Tools -> Split -> ... have a split window, the others don't have one, and activating a tab automatically (un)splits the window. Right?
Personally I prefer the current behavior, but per-tab splitting is better in some situations.
the plugin should probably concentrate on splitting the current document, wheras in general, a more flexible document/window/tabbing interface would be the better way to go. see my comment there: https://sourceforge.net/tracker/?func=detail&aid=3366108&group_id=222729&atid=1056535