So... I just installed Simpleviewer.
The Manage Galleries page only lets me Delete All Data, Set Defaults, or Reset Defaults.
Clicking on any of these seems to achieve nothing after the confirm box pops up.
There is no "Add gallery" option anywhere I can see.
There's an option for adding a Simpleview gallery in posts, which gives me a bunch of ugly thumbnails stuffed into the top of the post (identical to clicking "Add Media" in a post) ... and no gallery. Clicking on any thumbnail just displays the image wrapped in the WP template... e.g. standard WP functionality.
Sorry if I sound disappointed... this is the fifth WP Gallery plug-in I've tried that doesn't appear to have undergone any UAT. :(