There is a very common misconception at the actual purpose of a dynamometer. They are not designed to put out the same numbers across various machines in various locations for bench racing. The same model dyno manufactured by the same company can put out different numbers.
They key is understanding that the dyno is not much more than a gauge. It's there to take measurements. The most crucial element is that one dyno will provide consistent readings, so changes in power/torque output can be measured. This is the only purpose of dyno.
Dynapacks remove certain variables which can alter results/consistency including tire slip, tread condition/hight, amount of torque applied when tying car down (creating more friction), etc... Measuring at the hubs is the closet thing to an engine dyno.
Also, I cannot speak highly enough for the integrity of Church. I've been working with them for nearly 10 years, and it's been nothing but the best. There's no PR, no yupyism, no videos, no sponsorships, just people who love working on motors.
I started working with Mike prior to the inception of BPM Sport. He's as much of an enthusiast as any of us are, and is more interested in making more reliable power on an M3, than selling a product. He's been great to work with, and a great friend. All my overly engineered German cars have been tuned by Mike flawlessly.