If this is properly optimized, it should require much less finger movement than handwriting. And it can easily get even casual users to higher accuracies than even full size keyboards- the recognition is much more accurate because of the four quadrant, set, layout.
Even with a pen/stylus, handwriting is only about 30wpm. Moving to a finger would cut that in... half? worse?
What I love about your comment is that it has an actual speed.
The answer on this is simple. Take random groups people. Give group swype, give another group this. Train them for 10 minutes and test them. Report speed and error rate, bindfolded and normal. The train them for another 20 minutes, retest, then 30 minutes a day for 5 days and retest.
I doubt any group will get to 30wpm blindfolded.
Have a space at the bottom that is big enough to write two characters, so the system can know when you've started the second character, you are done with the first.
I could write with that super fast. And HW recognition is probably better, for most people, than their mobile phone typing accuracy.