Just a word of warning....make sure you have a very flat and smooth piece of road where you can do a standing start. The AP22 is probably accurate with the tenth of a second that the manufacturer claims, but only if there are no changes in gradient during a run.
Because it measures acceleration and deceleration g forces, if you start your run on the flat and go up a small rise in the road during the run, the unit will record it as a sudden increase in acceleration as the car tips back. Vice-versa for going downhill during a run.
A good buy? Yes, definitely, especially for measuring the difference modifications have made, but be aware of its limitations and dont take the figures as gospel! If you want pretty much infalible data, get a VBOX (but they cost a fortune!)