My Take
I do not think it would be a good tool for complete learning of a subject, but I do think it can be used to give a good background understanding. for example, if a teacher were to be talking about the Great Depression in class, in a VoiceThread, they could explain the economic climate leading up tot the depression and the Dust Bowl as well. this allows students tot learn what else is happening or leading up to a historical event, so that, in class, the finer details can be taught because students have the background. Lectures can also sometimes get boring, so students might check out while listening to a voicethread.
How I Use It
I have used this to listen to lectures at home as homework. this allowed for us students to come back to class with questions ready and the necessary background knowledge on the things we would be learning in class that day. I also think that it would be good for group projects so that the added level of presentation anxiety does not hang over students.