That’s the order in which you can create delight when you are talking about a feature to your customer/prospect. Mock screens trump words and working product trumps mocks.
If you show your prospects/customers a slide deck about the feature you are not gonna impress them, that should be the last resort. Mocks are one step better than words, at least then your customers can see how the end product is gonna look like, you might be describing a elegant horse and she might be imagining a donkey! Without the mocks the customer is not gonna understand the value well. With mocks, at least you got them to see what you have envisioned, this also helps you validate the user flow that you thought was the right one. The best conversations with the customer, which will deliver delight, is by showing a working product, it could just be a beta activated in your account.
Having said that, if you want to validate something quick, then mocks are the right middle ground between you describing the feature with just slides or words and going the whole 9 yards to build out the entire feature just to get validation.
Another lesson I learnt this week, was when you are talking to a prospect, always keep showing how the value is delivered in the product even as you talk about different value propositions in the product.