It's fascinating to me that all the information required for the analysis is publicly available. This seems like a big shift from an era when only an intelligence agency would have been able to perform this sort of analysis.
You can find a lot of individuals and small orgs on Twitter doing stuff like spotting military ships and their cargo, spotting drones on satellite imagery, collecting lists of destroyed heavy weapons, listing ATGM attacks, airstrike victims (airwars.com), geolocating videos/pictures posted to social media, colleting info on chemical attacks (bellingcat), collecting and publishing ISIS documents online, recreating 3D models of some events from public videos/photos, etc.
One example of 3D modelling (they call it forensic architecutre) based on open source data is in this report on Douma attack:
https://www.nytimes.com/video/world/middleeast/1000000058408...
Bellingcat is also a great example of what it shouldn't be. Most of what is produced is misleading at best. Some of the core "experts" (i.e Dan Kaszeta) are closer to propaganda generators than genuine researchers or informed sources.
If you followed Higgins prior to Bellingcat (back when he was "Brown Moses") you'd know he had a strong bias for the rebellion which has since just turned into a strong anti-government bias, strong interventionalism and explicitly anti-Russian.
A great example of how their bias slips into their analyses is examples like the fake sniper boy[0] which fooled a lot of anti-government "experts" to the point where people like Higgins tried to organise witch hunts against the scene director.
[0] https://journal-neo.org/2014/11/27/what-the-fake-syria-snipe...
As for Hexamine/Sarin attack/Postol issue: Hexamine was found in Sarin attacks by OPCW, it was declared by Syria to OPCW. Postol is not a chemist, nor CW expert, nor on the ground, nor very credible wrt his claims about Syrian chemical attacks, as several of his claims were already rejected by OPCW, who found Syrian regime responsible for the April 4 2017 attack (Postol had all kinds of theories about this attack). I prefer OPCW's conculsions to some random profesor's taking sides and judging from a distance.
https://www.armscontrol.org/factsheets/Timeline-of-Syrian-Ch...
You quoted Partisangirl, and I just can't take her seriously as an unbiased source either. Just one recent example of clear bias: Despite big civilian protests last few weeks in Idlib, she only tweeted one picture of some marching jihadists. She's very clearly pro assad-regime, at the expense of truth, accuracy, and peoples lives for that matter.
So yeah, Higgins is biased, but quoting other biased, non-expert sources doesn't really improve the matters.
Re: fake sniper. The experiment can be both revealing of reporting bias and highly irresponsible. People criticized the irresponsibility angle at the time. Witch hunt seems to be your interpretation.
I appreciate that you might have issues with the author of that article but it's not what I was going for. It's unfair to suggest that I'm quoting biased sources when I didn't quote them, just merely wanted to provide context of which video I was talking about.