I've just ordered one because it seems so much easier than having to tow the caravan up a ramp while checking if it's level. On some occasions the handbrake hasn't held it once the car is disconnected. In fact I have often use the jack to lift it level, then jammed the ramps undert the wheel to support it. the trouble with that method is that the level changes as you lower the weight back onto the wheel.
I've also ordered this one rather than the cheaper ones as it's aluminium and saves weight.