Use(s) Material is not Suited For: Tutorial (without additional text)
At high mass ratio (or high speeds), the balls move through walls and each other. This is easily discounted with a word of caution, but even at low speeds, the walls will move off the page, allowing for a little bit of confusion.
The lack of units reinforces bad habits of undergraduates,
who tend to ignore units.
General Comments on Effectiveness: Overall this applet has a good potential to be effective in teaching the concepts of collisions in different reference frames. Its effectiveness for self-study could be substantially enhanced by including assignments or suggested items for students to look at.