Do these forearm strength things work?

Something like:

http://www.uxcell.com/spring-hand-grip-exerci se-forearm-strength-builder-red-p-15484.html

Something like that, maybe even one of these:

http://cgi.ebay.com/Cando-Digi-Flex-Hand-Fing er-Exerciser-Blue-7-lb_W0QQcmdZViewItemQQ_trk sidZp3286Q2em20Q2el1116QQhashZitem518251695bQ QitemZ350078724443QQptZLHQ5fDefaultDomainQ5f0 QQsalenotsupported

Do these things work to increase forearm strength? I'm a cashier and i find i have trouble lifting things with my forearms when i have to reach. I sit at a desk for 6 hours or so a day and i thought this might be a cool way to burn some more cals too. Any advice?

For some value of work - grip strength is one of those odd things where you can actually increase it by training at about 50% of your max capacity where almost any other muscles need to cross a 60-80% of max threshold.

 So you could probably increase maximal grip strength with them  for some time, though working with thick-bar deadlifts and chinups will also serve to increase grip strength, so will using the old-school forearm rollers, wrist curls, plate pinch grip and similar exercises.

 I'm wondering though - is it maximal strength you need to train, or is it strength endurance to be able to lift a relatively low load for long periods of time? For strength endurance, trying to work with the same load and increase the duration of your exercise is actually where it's at - in which case yeah, working your way up to using the grippers for 5-10 minutes at a time will be useful for that particular purpose. Otherwise, I'd rather recommend wrist curls with dumbbells.

Yeah i just wanted something to increase the duration that i can hold. Sometimes i find that my hands get tired when doing a pull down exercise before my arms do. Thanks.