Hey, I fought with/against you today, I was using the same. It was so weird seeing another dynamo user.
Dynamo definitely shines in splat zones, 2-3 swings and the zone is yours. It's got so much range when you jump with it and it deflects splattershots(I don't think it deflects charger shots though). Even if you don't kill them from a distance, they're immediately surrounded by your ink and forced back.
I think people who try it once and dismiss it are trying to play it like a regular roller.
EDIT: forgot to mention my ign: kinetic
I definitely remember seeing a kelkador using gold dynamo in urchin underpass, there was one guy who was really good with splatterscope too in those games(think his name was AJ, really kicked our *****)