I tried both of these with no success. I thought I was ready and my daughter too...but neither of us were. The way you truly find this out is when you sink money into one of these things and it doesn't work. You can't know until you try it. In my case, 6 months later, out of the blue she started always going in the potty. Poop one week and pee the next, awesome and completely unexpected.
Unfortunately, this is my only child so I don't have a lot of basis of comparison. BUT my thought was and still is, that if you are convinced that your child is ready and you are too, then what could spending $20 or whatever the cost is now hurt? One thing I appreciated about these e-books was that they did give a "child's" view of what's happening which was very helpful to me.
Word of caution, Lora Jensen now spams me at Christmas time trying to get me to buy "letters to Santa". Thank goodness for the "junk" function on my email :)
Good luck!