Being visually impaired and needing such a tool, and by the way, I think it is great, I have the following scenario
Laptop has native resolution 1366x768, external 23" monitor has native res of 1920x1080 (it's just getting impossible to get anything less).
Till this week, I had screen resolution for the external monitor also set at 1366x768 despite the slightly fuzzy text, so this VMG problem did not occur.
However, this week I have set the ext monitor res to 1920x1080, and the DPI to 145%
Now when I use VMG, the whole desktop is resized (it looks like it only shows the top left 1366x768 of the 1920x1080, and the remainder of the desktop is not visible on the ext monitor (presumably this has something to do with the laptop native resolution being 1366x768) so I can't use the glass (VMG) on the rest of the desktop!