I haven’t used UXPin’s latest release, but I have used it in the past. I am a little confused that you want to use it along with Sketch? UXPin is a full wireframing and prototyping tool so you wouldn’t need to use both.
It’s easy to learn (drag and drop interface). There are lots of things that are good and some things that need improvement. Since it is not hard to learn I suggest signing up for a free trial and seeing if it works for you.