Some accounts say the layout spread the weight more evenly over the four wheels and tyre life was extended as debris did not damage tyre walls as much as it did with twin wheels when for instance stone or bricks jammed between the wheels when on sites, not sure this claim is valid though as they still got punctures no more or less than twins. The advantage was an extra Ton was gained on the axle weight, I suppose they filled a gap in the market at the time and plenty of companies ran them. Back to the Mercury though I thought they did look a nice balanced outfit when coupled to the 28ft Single axle type with the axle positioned at the extreme rear of the trailer or with the very short Dumper types.