To develop that big flexor/pronator belly, you need to use wrist flexion. Really heavy wrist curls bother a lot of my lifters' wrists, so we usually go for sets of 8-plus and seek a pump rather than maximal strength.
Wrist rollers are better suited for heavy wrist flexion, and this version is especially challenging since the resistance increases as you roll.
Take your lifting preparation as seriously as you take your lifting. That doesn't mean you have to devote half an hour to it. Here's what to do instead.