Author here.
The tutorial succeeds if it gets people to have a superficial comprehension what Vim is about -- especially for those that have been putting off trying it out in a terminal. That's it. It doesn't really try to make you actually learn Vim.
As a tutorial it could be made so much better. I don't have the energy slots for this project. But I feel anxious when I get feedback because I feel like there's some moral duty to fix the site. The least I can do is to pay for the hosting so that people get to have a go with it as it seems some people like it.
Just to make clear: the Vim behaviour is modelled and is not just trivial precoding of keystream. There is a sandbox where you have contextual helper at the right side of the screen. You can play around with it to your heart's and battery's content. But it is merely a simplistic version of Vim.
Development-wise the most fun aspect of the tutorial was the DSL for tests.
For some reason (haven't really updated the code properly in years) many fails. But click on the individual tests and you see something fun. http://openvim.com/tests.html
See the corresponding code here: https://github.com/egaga/openvim/blob/87b9e1d62c4144c958ddf8...
The actual code is modelled operating on html elements. This was a fun side project, so please don't be too critical. It grew bigger than anticipated.