Been training for 22 years now and would have to say this new product called Grip4orce that I picked up from the Arnold Classic has made arm day insane. I'm now getting pumps like never before.
You can't see it visually but these hand held Grip4orce attachments has resistance built inside, pretty crazy. Also I've noticed my strength has gone up when I go back to the normal bars. Typically I straight bar curl 135 for 10-12 reps now 18-20 reps in only four months.