Yes John thats what Ive used to measure our disc speed

A simple optical tacho (I used it for my model aircraft) ..you just stick a white stripe down your disc (or any contrasting colour)....it is VERY accurate ..I measured the rpm of of my bench circular saw by painting a line of tippex on it and it was spot on the makers rpm.

You do have to be pretty close though ( 6 inches or so)and though I felt safe measuring Chips rpm at home, I dont know safety wise whether it would be advisable at an event.

Eds laser system seems like it might be quite safe as it seems it may have a longer range (what is the max range of the laser pointer Ed?)

But as mentioned they are very accurate.

Tom