It's hard to conceive of any credible criticism of the Muzzle Brakes & More testing apparatus, for purposes of direct comparison of the reduction in rearward force (recoil reduction) of the various muzzle brakes on the individual test rifles.
The method doesn't separate out the multiple recoil reduction design factors that could be in-play on the various muzzle brakes. Do I care about that? Not really, other than for the sake of curiosity. I don't feel the need to know the minutiae of cause and effect for my purposes. The test apparatus informs me of the comparative recoil reduction of the various brakes tested, no matter the manufacturers claims, or other users claims. Just the final result captured in a simple, straightforward, unbiased demonstration of comparative recoil reduction.
I wish such a simple demonstration of the accuracy of factory rifles, or custom rifles, were available. Would make rifle shopping so much simpler. Of course, many more factors are in-play when it comes to the average accuracy of a rifle. Comparative muzzle brake efficiency, on the other hand, is quite handily displayed with a straightforward video, such as those provided by Muzzle Brakes & More.
I eagerly await Nathan's next round of videos, comparing another slew of muzzle brakes as tested side by side. It may not be the equivalent of Paul Harvey's "The Rest of the Story", but it's all of the Story I need, prior to purchasing my next muzzle brake.
When it comes to pressure wave blast and perceived decibel levels causing headaches, I'm afraid no such simple test will ever exist. I've got a MB&M 5-port brake on my 338 Rogue. Never experienced a headache from shooting it. On the other hand, I have suffered headaches from excessive recoil in the past, from a 7lb 375 Weatherby. 1st shot was punishing. 2nd shot no better. 3rd shot I'd had my fill of fun. 5 minutes later came the headache. Never shot it again, until a Muscle brake was installed. End of headaches. So I consider myself fortunate that I don't (so far) suffer from sound wave induced headaches. Would take all the fun out of it, for sure. And be cause to purchase a suppressor.