If your product makes your users feel stupid they will not want to use it. Ask them questions like “On a scale of 1 to 10, how confident do you feel using this system?” Get to the heart of things with your questions and you will no which way people lean on the usability of the product.

“So I propose that we all ask one simple question of as many potential users of our products as we can. The question I asked above was “On a scale of 1 to 10, how confident do you feel using this system?” But in truth, the question itself is less important than making sure you ask it. It’s a well-understood quirk of human nature that we tend not to take things seriously unless we’re measuring them. Whatever you ask, pay attention to the percentage of scores that are under 7. Those are all the customers you’ll lose, customers you’ll keep without delighting, or customers you’ll perennially frustrate, and for an embarrassingly fixable reason. It’s easy to do, and it might just move us toward a more usable world, which I know my mom would appreciate. ” – Roderick McMullen (fastcodesign)
http://www.fastcodesign.com/1668923/usability-is-king-for-you-product-heres-how-we-can-finally-measure-it?partner=homepage_newsletter