1) What kinds of information and insights did it give you about the usability of the prototype?
This technique gave me more insight in to the small gestures and the body language of the user that you could easily overlook but could be very helpful in informing how someone might sub-consciously perceive and object and their interaction with it.
Think aloud is excellent for getting raw and instant thoughts and ideas from a user about something. I like the candid responses it could elicit without the user realising. It also highlighted their thoughts and frustrations. Even though it isn’t natural for the user I found the more they did it the more open they were.
2) What aspects of the technique worked well or were frustrating?
It is tricky to observe and note at the same time and almost needs to always be captured in some way so you could reflect and look back on the exercise to pick up anything you have missed.
There is also user bias and the desire to appear more positive or please the person conducting the exercise.