When you're talking about STV, the most important reason that STV is used mainly in relatively small districts is not to have too long lists of candidates that may be confusing to the voter. Of course, for the voters it's still not terribly complicated, because as long as they find at least one candidate they like among all of the candidates, they can vote for that person. They can also have a second preference, third preference, and so on. But in any case, when you have a five-member district, for instance, it's likely that several parties will nominate several candidates, so I don't think the list would have more than, say, 10 or 15 candidates. With MMP, there are not likely very many candidates in a single-member district, so that's not a problem. Then for the party-list candidates, it's the parties that present lists, and you vote for a party rather than individual candidates, and I think that's still not all that complicated.
On August 22nd, 2016. See this statement in context.