A fan of the “Tac-Con 3MR trigger system” comments:

“…It does take a little practice to master, however I was able to pick up a sample rifle and immediately knock out very quick 2 and 3 round bursts. If I had to guess the cyclic rate, I would way it was in the neighborhood of 500-600 rounds per minute (M60 speed). You can go faster or slower depending on your level of experience.
….
What I can say so far is the system worked VERY well for me on the range today. I was able to fire 4 magazines through two different demo rifles and by the end of my time on the range I was running the guns at probably 700+ rounds per minute.”