I just love doing the seated two dumbbell curl, but I would like to know for sure that I am performing it correctly.
Please tell me (1) is this a worthwhile exercise (2) how you would recommend its performance.
I think that the seated two dumbbell curl is a fine exercise, second only to the Scott Bench Curl, or Gironda bench curl (depending on your age).
The way I perform it is cross-legged to prevent the upper legs interfering in any way with the path of the dumbbells.
The biceps must be allowed to curl the weight in the purest arc possible.
I also try to keep my upper arms still when I curl. Do not raise the elbows up at the conclusion of the curling motion.