For many years now we have refused to supply or install kits where the left and right circuits are joined. This is on the grounds of safety primarily but also linked to legality. An air suspension circuit where the left and right are joined leads to air transfer as the vehicle corners which is dangerous as the vehicle progressively rolls (leans) through the corner getting worse and worse until the car can potentially spin out of control. This is worst on fwd vehicles but affects the handling on all vehicles.
Other suppliers are not so discerning and are happy to take your money and supply items not lawful for road use. Does this approach cost us sales – potentially yes. Are we going to change the policy – definitely not. It was heartening the other day when consulted on documentation for air suspension to see that the Australian government holds the same views as we do and wont issue permits for vehicles with conjoined systems.
It is dangerous to use FB or Front-Back systems where the left and right circuits are joined. It is almost certainly not lawful for UK road use (regardless of any MOT you may have) and saves only a relatively small amount of money for such a large safety compromise. Independent systems handle better and ride better.