Just updated VASSAL and VASL to try out this extension. It seems quite nice.
I noticed it doesn't seem to interact too well with the "Hideable Control Markers" extension, though. In my current DZ:SME campaign, I am using this extension to mark setup areas with the thick lines that normally line up with the hex borders; this works great since they can easily be hidden during play, and will let me use two different colors on different sides of a hexside. But when using the BoardZoomer extension, these lines will not zoom (they remain at counter size) and so will turn into discontinuous lines.
(Of course, where this extension will shine is with small-map, high-counter-density scenarios. CGs, where you have to mark perimeters, usually use large maps, but they can have some pretty high counter density, at least in some parts. Well, if this cannot be easily fixed, we can just zoom back to 100% for the perimeter drawing)