Pretty good on the iPad but heres the catch...

It is free, however...I found this info inside the app.

"With a free subscription (available by default), you can use Mapster without charge. However, you are limited to downloading 200 tiles per day on an iPhone or iPod, or 500 tiles per day on an iPad. If you try to zoom in on an area that you havent downloaded tiles for but you have reached your daily limit, it will just appear blurry. After midnight, you will have another 200 or 500 free tiles that you can download."

wxtech1 about Mapster