I have no dog in this fight, just sharing my experiences.
Another fun chain brake story. Local Sunbelt rental has 290s, 291s and 390s. I was returning a mini excavator and another contractor brought back a 390 he had just picked up and told the counter guy it wouldn't run right.
One of the mechanics grabs it and takes it in the shop, I followed him out with my safety glasses after settling up. He has it on the bench with a screwdriver in the carb raising the idle and trying to blip the saw and it just grunts with no chain movement so he turns a little more. I wave my hands at him but I am not heading into the work area and he doesn't see me. After he has the saw screaming and smoking he shuts it off. He looked over at me, they all know I am a saw nerd, he said what's wrong with it? I just said chain brake and he flipped me off and got back to retuning the saw
A guy can rebuild track hoes for a living and still forget simple stuff.
Stihl rep showed us an inertia brake in action at the service day last week, he took a new 291, clicked the brake off and dropped the tip on the ground, the slight impact made it trip, as it is supposed to. A chain brake can stop a chain in a tenth of a second at full throttle but at low throttle there maybe more torque? I just know you can rev up a saw and smoke the brake band from idle on many saws.
Dave