Well, the truth is that nearly all PR electoral systems look pretty complicated from the outside, if you try to understand them in every detail, but for the voters they're all pretty straightforward. I really can't think of any electoral system where the reports have said the voters found this just too complicated. They're all fairly straightforward for the voter.
Now, under PR-STV, voters can say a bit more about what they really think. They don't have to just say, “Yes, I like that one and I don't like the rest”. They can rank all of them. They can say, “This is the one I like the best and that's the one I like second best” and so on. They give a bit more information and because of that it's a bit more complicated, but really it's not in any way too complicated for voters to be able to do what they're meant to do.