I know this is old as hell, but I might as well explain my opinions on the Null Mysteriis:
"The compact comprises a large bulk of rational, science-minded or academic folk: biologists, chemists, physicists, and the like. In recent years, however, the compact has seen a growth of pseudoscientifc efforts amongst its hunters. We'll talk more about that shortly, but for the moment it bears examining how hunters get from science to pseudoscience (and beyond).
Scientists seek rational explanations that are proven through rigorous testing. The scientifc method is everything. Success is inevitable, even in small ways: vampire blood looks a certain way under a microscope, or electricity has reproducible effects on reanimated human tissue.
Problem is, the World of Darkness is home to all manner of unexplainable horrors, and these horrors consistently evade rational explanation. The truly diligent don't take that as a failure, and continue to pursue explanations.
Some, though, aren't truly diligent. It doesn't help that studying the horrors of the World of Darkness means a life besieged by… well, horror. That damages the mind. It winnows one's devotion to reason. Answers are a lot easier if you soften the rigors of one's standards, yes?
And that's what happens. Eventually, science gives way to pseudoscience—proof obtained through less meticulous testing and with reason that crosses over into unreasonable territory."
To me, the description of the "rationalist" faction makes them sound like the Hollywood concept of what a scientist is in a supernatural setting - namely, that they're basically priests in the Unified Church of Science, treating anything that doesn't fit into the world of electrons and radio waves as heretical nonsense that can't possibly be anything but a misunderstanding of the shining, Pyrean laws of Science which all things abide by.
Now, an actual rationalist would respond to vampires and werewolves and witches by reanalyzing their concept of what rules the universe runs on - which is where my assertion in the previous paragraph comes in: their founder is described as treating anything that moves outside Harvard bounds as being 'pseudoscience' and thus unacceptable, which is quite a bold claim when he's trying to study phenomena which generally seem to either be truly chaotic in their behavior (i.e., their existences represent
defiance of the laws of reality, rather than obedience to laws not yet discovered), or involve forces and principles which the modern scientific community does not have the technological capacity (and perhaps not even the conceptual foundation) to measure in any effective manner.
In other words, any biologist in the World of Darkness who decides to try and expound on the physiological functions of the
Uratha is talking out of his ass, because werewolves in WoD are spirit-and-flesh hybrids born of a wolf-god and the Moon, with about as much connection to modern scientific
anything as the color octarine. He has neither the knowledge, nor the tools to acquire that knowledge, unless he starts dabbling in sorcery and mysticism, which the
Null Mysteriis appear to poo-poo as claptrap and obfuscation.
Pseudoscience is honestly the Organization for the Rational Assessment of the Supernatural's best bet, but it's still not a very good one. Sure, Kirlian photography and orgone readings might actually yield benefits in certain cases, but the old guard are also fairly right about most pseudoscience lacking enough rigor and specificity to be viable.
Unfortunately, that just amplifies the real problem their compact faces, namely that their underlying mental paradigm is, well... it's rather apropos that their origins lie in the Victorian era, given the level of intellectual colonial spirit in their beliefs. The Null Mysteriis does not come across as wanting to understand the supernatural, they come across as one of the less-kind interpretations of the old Technocratic Union, hunting down reality deviants and then trying to forcibly crush them into a box made of technobabble and presumption*. They want to understand on
their terms, not the universe's, and that shit doesn't hold water in a world of Astral Realms and invisible vampires.
Take their Stereotype section for an example of what I mean. Now, rereading
Hunter: the Vigil in 2017, I've long since realized that the Stereotype sections were a hideous mistake and are just generally garbage, but dear Lord 2012 me didn't feel any better disposed toward the
Null Mysteriis after reading theirs. It's catty, sarcastic, "coolest guy in the room" bullshit - a tour de force in douchery that radiates smugness, even by the odious standard of other Stereotype sections - the ones for
Beast: the Primordial were marginally worse, but only in terms of provoking emotional outrage.
To be blunt, it's the Mysteriis sneeringly dismissing every other compact as either imaginary or delusional, with exactly the same air of entitled elitist condescension of a guy on the Internet jeering at the sci-fi/fantasy genres for being silly and unrealistic.
Here's a nice sample:
[About the Aegis Kai Doru] Let me get this straight. There's a conspiracy that's at least 2,000 years old, right? And it's got the head of John the Baptist and about a dozen other ancient holy relics, right, all hidden away and guarded by this hereditary sect? And sometimes they come out and use them to fight monsters? That's not a plausible scenario - that's The Da Vinci Code.
They then go on to patronize the Loyalists of Thule as being 'an object lesson in how an obsession with the supernatural can make one
all too gullible' and crack wise about
The Omen when mentioning the Lucifuge.
Again, the Stereotypes are a shitty WWism, but it still creates a certain impression. A very poor impression, that makes the Null Mysteriis sound like arrogant know-it-alls who wouldn't be caught dead doing anything as scandalous as actual serious consideration of the supernatural's existence when they could just smugly proclaim their omniscience from their academic mountaintop instead. They're not the Ghostbusters; they're Walter Peck, waving away the protagonists' "silly notions" and then making the situation worse as they refuse to adapt their methodology and ideology to a scenario where they just don't apply. As far as I can tell, the only way to make them playable is to strip out all of the legit supernatural components of the World of Darkness and have them fight
The Strain or something - because otherwise, the entire party gets ripped to pieces when the "hemophages" don't fall unconscious when injected with tranquilizers, and instead decide they'd like to see what color the party members' viscera are tonight. As-written, they're just too genre blind and, well, Hollywood scientist-y.
I'm legitimately curious how your DM handled them to create such a positive impression,
@ManusDomine.
* This is not helped by the fact that their opening fiction describes some Mysteriis members stalking a werewolf, cornering him in a bar he frequents, talking dismissively over him about lycanthropy until their veiled "we know what you aaaaarrrreee~" bullshit pushes him to get physical, then tranqing him. It ends with them "bringing a truck around" and getting ready to start testing some theories on the poor bastard once they've got him properly strapped down in their lab. 
