I am a subscriber for a WDH.
Never tried airbags though.
I have always struggled with the entire concept that the purpose of these two options is interchangeable.
I have tried to justify this with some form of scientific background trying to troll for answers on the Internet but nothing. So why is it that a WDH which purpose is to apportion the load more evenly across the entire rig is interchangeable with airbags which I thought was for a stiffer ride and prevent sagging in the back with a load.
So there is the can of worms. Bring on the comments.
Its a touchy subject just like 10amp plugs

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Essentially by putting the van on the back of the car weight is taken away from the front of the vehicle which reduces breaking ability and gives much lighter steering. Try it for yourself, just a heavy trailer on the back with no wdh or airbags and you will feel the steering is much lighter and breaking more difficult in turn.
I have experienced this even with a WDH but I have not put it on the right chain link so its not setup right.
To correct this you have to transfer the load back on to the front of the car to improve steering and breaking control.
The school of thought is that a WDH not only lifts the rear of the vehicle but transfers the load back to the front of the vehicle.
The school of thought on air bags is that it only stops the rear of the car from sagging but does not actually return the weight to the front of the car.
There is many schools of thoughts on what is correct or not correct but this is a generalised view of what people consider.
For me personally my intention of the air bags and testing was to tow without and without them pumped up.
I can honestly say in my experience without the air bags pumped up I do notice a signifcant difference in steering capability and braking ability.
With them pumped up it is corrected, that said my ball weight and tow weight overall is not very much compared to some of the bigger vans so does not apply in all scenarios.
All said and done I find it a pain in the backside to carry the compressor and air gun and have to pump up the air bags where as the weight hitch was just two bars, snap and your on but I also did not like the constant cracking noise coming from them.
So happy medium I am on air bags and so far happy with them.
I will point out again that not one ruling governing body has stated you need one or the other to tow legally and even some manufactures recommended against using a WDH from either the vehicle completley or with there tow bars even though they have 3+ tonne tow limits.
Again its all subjective and really until a governing body implements a study for and against and rules on one or the other then its purely subjective and experience based.