This trainer works for the limited scenarios given in the book, but has a very limited instruction set and error messages that are incorrect. Legal router instructions result in error messages. I would not recommend it for anyone that has any kind of alternative. Some commands also don't work properly. If the bugs were fixed, and the simulator followed the book better, it would be a great way to practice.
Nothing beats hands on experience.
If your objective is to pass the CCNA test shkip this altogether. This can be very confusing to a student who is attempting to learn router programming. Todd Lammle's book is excellent, but, in my opinion, this product is week. Loads of potential here, but it needs work. Most Cisco technology students cannot afford to buy routers and switches to practice with, nor do they have access to such network devices at work.