Well i dont know what the other guy in this review is talking about, but if your going to actually USE ASL, you will quickly realize deaf people spell fast haha.
Now of course deaf people are aware your learning and will slow down (i love how nice they are :D). But i find this tool very helpful in getting your mind set on fast spelling and giving attention to when spelling is used with ASL.
If u get to the highest speed, you start to guess the word after a while, even though the words were going by too fast for you to see. Again ASL is heavily context base when it comes to signs in general. So you will substitute the word in there spelling (unless its a name or place of course, but even then theres a chance you can guess the name by seeing a few letters)
I recommend this app to annnnyone learning ASL.
Hope this helps you decide :)
Takecare and have fun :D