How do I set the export persona to mm?
I can confirm. Snapping Manager does nothing, slices only snap to themselves and to spread & mid points.
Looks like a bug to me. @MEB?
A quick'n'dirty workaround:
in Photo persona, create transparent (e.g. a "50% red overlay") vector rectangle shapes of the exact size of your slices
switch to Export persona and "convert" those rectangle layers to slices in the Layers panel
uncheck them so they don't export, you may want to name them something meaningful to keep tra