Found the problem!
It’s Page Builder by SiteOrigin that’s in conflict.
So you can’t use the 2 (at least not in the latest (4.6) WordPress.
After deactivating that pagebuilder, this plugin works.
In Firefox (48) it isn’t totally smooth (Chrome/Safari it is)
when you use the slider (even doing it slowly)
but it is if you use the click method (clicking on the far left or right
side will automatically slide the slider to where you clicked and smoothly).
There’s also a watermark and URL in the bottom right
(better would be if the author made a more extensive premium version as well
and advertised that, solely in the admin backend).
But nice plugin overall.