Dyslexia is a learning disorder that makes it difficult to read. You may already know that, but it's hard to understand exactly what that means without experiencing the disorder yourself.
This example doesn't necessarily apply to everyone with dyslexia, since it's a condition with a spectrum of more than one symptom. One person with dyslexia commented on Widell's blog that his dyslexia works differently — letters shift up and down instead of side to side. Others said their dyslexia is more or less severe than the simulation. Some said the simulation wasn't accurate in any way for them personally.
Still, the simulation is a good way to introduce someone to the concept of dyslexia. It definitely makes it much harder to read — and that's one of the things educators and peers need to understand when dealing with someone who has dyslexia.