It's a poor design that doesn't allow spring tension to be changed without changing gap/striker or disassembly and shimming, and I don't see how he changes his gap with this, unless I am missing something....
This isn't a free flight hammer either, its an SSG
Free flight "ssg" would allow the hammer to freely fly separately from its guide and spring, this one travels all as one unit, hence its really not a 'free flight hammer' design.
That's in my opinion at least.
I would prefer a design that allows the hammer to fly by itself. This method adds a ton of hammer weight which increases dwell big time and requires more spring to keep it moving at a decent speed for proper lift, you can see his struggle to "cock" it one handed, while I can toss a weak spring on my ssg, cock it effortlessly with my weak hand and still achieve max fps when using stock hammer weight, albeit on air gun regulated @ 1900-2100 psi