I dont want to buy, but thats because I already have one!
For those that dont know, they are like those G-Tech things you can buy for your car... except the Apexi one is more accurate.
I can definitely recommend, however do yourself a faour and get the g-sensor as well. Very accurate 1/4 mile times (Apexi vs actual Eastern Creek Runs= equals difference in times not exceeding 0.2 of a second).
They also come in handy for circuit sprints because they got a timer in them as well.