Before you waste your money on this solution looking for a problem, my first question is what problem are you currently having that you think this might "fix"? If it's sumping, I can't imagine how an additional crankcase vent would fix the fact that the oil isn't being directed to the oil pickup in the sump and on to the pump. And btw, some pressure is normal in a crankcase.
If you really want to test this guy's theory, remove your oil cap and cover the opening with some medium to fine mesh screen material to keep debris out, then run the bike under the same conditions that you experience whatever problem it is you want to fix. If it doesn't fix your problem, his $129 vent won't either.
Jerry
Not sure they claim it will cure sumping, more help motor breathe better, well only another way to the same idea as T-man fits to his builds ( not just M8's, video on youtube)
Have seen the musings of the guy on M8 FB if iirc
Fitted S&S pump & plate, now his motor is over oiling the top end out thro head breathers
not sure if head gasket fail was involved, on a stock 107,
Note that S&S 124/128 kits come with redundant oil way plug kit
Note that Cometic revised it's M8 head gasket to cover/seal off that oil way