I love my BB18.
Here's my recommendations to getting used to it. First, get rid of any options you had set for your mouse. This is a completely different animal.
Once your thumb is used to the default settings, then start to tweak things as need be. I actually 'roll' the ball with my thumb, taking my thumb off of it, and then back down to stop the pointer when I want to get around the screen quickly. You'll get used to it, and I'm sure your shoulder and arm will thank you as mine do for dropping a mouse.