This gallery appears with a full-size image (first image in gallery) on your page and thumbnails to the left. Not good for a page where you want to have multiple galleries.
And if you do want to put multiple galleries on the same page, you have to manually create space between the galleries, otherwise the 2nd gallery overlays the 1st, the 3rd gallery overlays the 2nd, etc. And manually creating space doesn't work reliably from browser to browser or from computer to computer (to tablet to phone ....).
I use a watermark plugin on my images (client is an artist), but watermarks are removed from thumbnails, not a good thing.
Just wondering - Why would someone create a WordPress plugin and not use the WordPress Support forum? Not a fan of GitHub and I certainly don't want to join yet another website just to get support for one plugin.