The m600 and Blackberry keyboards work in different ways.
On the Blackberry, it's one key and it guesses what word you're typing like predictive text.
On the m600, you can press the left side for the left letter and the right side of the button for the right letter (or anywhere on the button for the number). The keys look quite bit and are shaped to make it easier, but I can't really comment on how well it works since I've yet to try one.