According to CST's site, this has "Mechanical Optical" tracking, so apparently not fully optical/laser, which makes this essentially an inverted ball-type mouse.
This would prolly best be hand-held like a remote, using the trackball with your thumb -- handy for casual surfing kicked back on your chair or couch -- but seems like mechanical tracking rollers would pick up skin oil and debris and need to be cleaned frequently.
At this price I might bite if it were fully optical, but my prior experience with mechanical tracking rollers on the old Kensington Turboball (its sole, and fatal, flaw) inclines me to give this a pass.