I love thumb! The thing I've discovered is
1. It really works best if you're holding the device.
2. Most any time you want to correct a word you already spelled it screws up the selection.
3. When you want to space in the middle of a word, it goes to the end of it then spaces. Like if you forgot to hit space and want to separate two words, you can't.
4. There are so many different types of keyboards in the settings that anyone will find what they want.
If you have you tablet on your lap or on a desk, or something, then it won't make that big a difference for you.