There is only so much travel on a shock , there fore the lower you go, the worse the ride becomes. The suspension is prone to bottom out and this is nothing to do with spring rates and the height the spring is set ! To improve ride quality and handling (at any height ) a proper well designed shock is needed . You can spend all the money on the fanciest shocks but if the car is too low the ride is crap and the performance shocks cant do what they need to . Coil over kits ( good ones ) do have good shocks but as mentioned in this thread when lowered to max the ride is worse . If you set a coil over kit to max height it is still lower than standard and should sit close to where a Lowering spring would sit . If this is what you want dont waste money on coil over kits buy a sport kit . "Sport shocks and springs" , this wont give knocking issues and adjuster threads that rust up and corrode .
The main reason for this recommendation is that the T 5 T6 configurations have several different spring rates . A coil over kit has one spring rate and although the height can be adjusted to get the desired look its possible that the spring gets pretensioned to a point where the ride gets hard or bouncy . ( see the picture on the B14 thread of the rear spring almost completely collapsed ) If you chose a sport kit you can select the correct spring rate for the vehicle and the ride is much better .
B14 is a mono tube design shock and very efficient ( not comfortable due to hi pressure gas ) the So low kit is the cheaper design dual tube shock which historically is more comfortable , but set to the lower recommendations will also be very hard on the road .
Transporter owners seem to think that the next step from JUST springs is Coil over, and there is always a comparison between Lowering springs and Coil overs these are very different solutions and shouldnt really be compared . The best set up is to optimise the lowering springs with a sport shock and the ride quality is great , we have sorted many comfort issues out with sport shocks and not coil overs over the years .
Its important to note that coil over kits were designed for racing cars . they enable low ride height , adjustable camber, and castor settings, as well as corner balancing the chassis . most of these features are Useless on a road going vehicle and definitely useless on a transporter , ( unless the camper is converted to a track day warrior )
The tuning industry has closed in on the height adjustable feature and exploited it to slam cars to the ground and make them less reliable and uncomfortable but LOOK great .