Kettlebells work better than dumbbells for flyes. Because of the position of the resistance, the pecs are under load for a greater proportion of the range of motion.
With dumbbells, the muscle tension on the pecs is greatly reduced at about 60% of the range of motion. This can make the reps less effective, especially when you're using a method where you must maintain constant tension to create an occlusion effect.
When I first approached corrective and performance exercise specialist Paul Chek about writing for Testosterone, his first concern was whether I'd choose to soft-peddle his article. In other words, he was worried that I'd try to "dumb down" his material.
It never ceases to amaze me how trainees like to talk two and a half times their actual size. Only in the gym will complete newbies rant about their Ronnie Coleman-like genetics before even entering their first Mr. Akron contest.