Mercedes W204 C63 Estate/Nissan GTR/M3 Touring (joined the fleet)
I had the C350 with a tuning box - massive difference with torque and also fuel consumption. Fitted several of these on friends n family cars and can personally recommend them (easy to remove prior to servicing as well)
Some will dispute how this little box can make a difference but, from personal experience, it does. And, for £125 it's worth a gamble (which was my thoughts)