The rule of thumb is, the thicker
the handle of an exercise device for use with the
hands—whether it be a wrist roller or a thick-handled
dumbbell—the more grip strength it requires to use it.
The corollary is that the
more grip strength that is required, the more forearm
development you will achieve.
Hanging
your arms down is not really a good idea.
You simply will not achieve
the same level and intensity that you will with your
arms held straight out, parallel to the floor.
Your hands and forearms will
exhaust long before your shoulders.
For more information on why you
should use a tapered, rather than straight, wrist
roller, see the page on the
The Tapered
Wrist Roller. --Mike