1.What kinds of information and insights did it give you about the usability of the prototype?
Doing a task in a website while observing carefully gives you a hint on where are the usability problems, since every person is different it is important to see by testing others too. If it’s just one person perspective or a key observation. It is difficult to start looking for the problems in a platform when you have no idea where are they. They can be everywhere. Setting a task is a really good way to find out about where to start. Then, begin to dig deeper, also, to have a general idea if you are going the right way or consider a redesign earlier without losing too many resources.
2. What aspect of the technique worked well or were frustrating?
I believe the frustrating part is understanding what is this technique for and what are you trying to achieve. Once your mind process the method you find it very useful, you start understanding which tasks are better to understand your user and wich ones are not worth of testing. Unfortunately, you can only learn this with practice. I personally like this technique very much. Couldn’t think about any better because it gives a structure to the learning process, but it is open enough to realize about things you may be overlooking.