The CBR was developed primarily for math teachers who want to quickly collect data. It connects directly to the graphing calculator to collect motion data. If you only plan to use calculators and only want to measure motion, the CBR is probably the right choice for you.
If you are a science teacher and plan to use the LabPro or CBL 2 most of the time, you should consider the Motion Detector, as it is less expensive than the CBR.
If you are going to share you Motion Detector with a math teacher, consider the CBR since both of you can use it either directly with a calculator or with a LabPro or CBL 2.