The NVH kit is supposed to reduce the Noise Vibration and Harshness, something that it is not very effective at doing at all. I think the main idea was to isolate the Bevel Gearbox in an effort to reduce the noise from that, it failed. I had the NVH kit fitted to my 2013 car at the same time as the Centa upgrade and noticed that this combination introduced some new vibrations and noises soon into my first drive after the upgrades. The main annoying new vibration was a "thrum" through the body, this was maybe more noticeable as some of the original vibrations and clunks from the Harley compensator had gone. It felt a bit like a worn UJ in the propshaft but wasn't.
The NVH kit was fitted again when my car had a chassis change to a post 2014 chassis in 2015. It all felt better (smoother) in that chassis but still had the "thrum". I fitted Phil Bleazeys BB mounting kit almost 8,000 miles ago and it improved things by eliminating most of the "thrum", smoothing things a bit more and stopping the big clunks when accelerating hard from a standing start. The car also reduced its weight by several pounds with the removal of the NVH steel girder. I cannot think there are any negatives with Phils BB mount, no regrets fitting it. I have driven some M3W's with the NVH kit fitted that don't seem to suffer the same problems as my car did and drive very well, really not sure why but some are much smoother than others.
3000 miles ago I got Phil Bleazeys Centa modifications and the car is now pretty much vibration free, apart from the big, lumpy engine on the front. You would have to ask Phil how many BB mount kits he has sold but it is quite a few.
