A few items that I have come across whilst working with Pro Galleries in Editor X. In general things work fairly smoothly, except for a few odd behaviours of the widget:
1) Depending on whether you remove all preset images first them play with setting up the size and proportions of your slideshow (when using the slideshow layout), height can either be set to fluid % or ONLY in pixels which brings it to the next point...
2) Slideshow doesn't scale proportionally even when set to fluid, and can not fill entire width of browser across devices.
3) Layout and Design settings of the gallery resets back to original default if and when it's moved up or down in the layers order.
Just a few things I have encountered and really look forward to release of new features.