I like this method; I think it's been around for quite some time and that I maybe even read it here before?
I'd like to add that I feel this method is good for churning out a large amount of lower quality content but less effective when you are trying to put out quality and well researched pieces. I believe that the bottleneck is not how fast you can write. You mentioned that an average person writes 30 words per minute, which is significantly lower than how much you can say in a minute. However, you can easily double that typing speed if you are consistently writing on a daily basis.
But to get back to my main point. It's not about typing fast; it's the amount of time you need to take to research a topic properly and understand it, to structure the piece before you start, and how much time it usually takes to get your thoughts organized before you say/write something in a simple manner that other people can consume.
This is, of course, easier if you are highly knowledgeable around the topic you are writing about and already have your thoughts and research organized prior to getting the words down. But if it's a less familiar topic, and you want to do this technique, you may not end up saving much time at all.