Not my favorite Shel Silverstein but still fun. My first time reading it, and it's similar but different than his other stuff. 
I think it's easier to read in your head than it would be aloud. 
I found that my brain automatically/unconsciously switched the letters back to normal half the time so I'd have to reread a bit. I think kids would find it funny but at the same time I don't think I would have found it funny when I was a kid.