Not sure if it has been covered but as far as running FWD cars on a dyno, when they really do put some power down it can be dangerous. Torque steer can walk the front of the car straight off the rollers. Also add that manual transmissions like to snap whenever someone 'drops' the clutch on the dyno. Just things to consider as far as letting owners run their own cars, there are many 'not so smart' hot rodders out there that may end up looking to you for why they're car took off or they're input shaft snapped. Also you'd have to make sure you strapped the vehicles down and set them up right if anything, thats another thing i've seen some hairy things done! Dont forget the big AWD crowd...those dynos are big $$$, depending on the car scene where you are, it may or may not be worth it.