My Take
As a programmer myself, I feel the concepts being taught here are essential. The languages can be learned later. The Hour of Code is a great introduction to see if kids are interested, and the K-8 Intro to Computer Science course, (which is going to be modified to K-5) is a great starting program. There are a few quirks that took me a while to figure out, and some bugs along the way that have been fixed. Teaching the k-8 program requires some practice on your part. Students always struggle on the same spots.
One of the most interesting things I discovered in this process was that a lot of my special ed students did well in this class, which gave them confidence. I had two level 1 ELL learners join also. Thankfully they can change the language, and I was able to help them, and make English connections.
I am looking forward to the new levels so that I can include more grade levels.
I use this program, along with Tynker, Scratch and Codecademy in my after school class. I do require they finish the Code. org course before moving on.
How I Use It
I did the Hour of Code at our elementary school and use Code.org for grades 3-6. I also have an after school coding club for grades 4-6. I signed my after school students up for the k-8 program. This goes more into depth and gives them a lot more practice.