Witch’s hat bits, in various taper diameters for the really stubborn o rings. Look up the Pana-vise. Very handy when working on the FX blocks.
Padded jawed pliers of all types are almost a requirement. Cordless battery powered screw drivers make life easy on the folks suffering with arthritis. Bore scopes are handy in looking deep into regulator tunnels.
Newman Buck, who owns 910/Capefear airguns, carries a few of the FX specialized tools. Metric tap and dies, along with M3 to M5 helicoil inserts and the required drill bits are really great to have “in case of”.
The saber tactical bottle valve removal tool is a must have, also, and lastly for now are the spring tensioned spanned wrenches, metric, that bicycle techs use, can be handy.
As far as torches for heating up stubborn fasteners I use a fancy cigar lighter, powered by butane.
If I find a tool that’ll make the job easier, not necessarily faster, I buy it. I’m done rigging makeshift doo hickey crap to make something work. Get the right tool for the job.