Anybody use those grip strengtheners?

I'm an engineering student and a climber which unfortunately means that I struggle to get to the gym regularly.  I'm thinking about buying one of those grip strengtheners like https://www.amazon.com/Kootek-Strenghthener-Resistance-50-75-100-125-150-Adjustable/dp/B01780EY2Y/ref=pd_lpo_vtph_200_bs_t_1?_encoding=UTF8&psc=1&refRID=KVC8XKQ58PTJ5TGCETTN 
or like
https://www.amazon.com/Black-Diamond-Forearm-Trainer/dp/B0000E675V/ref=sr_1_4?keywords=grip+strength+trainer+black+diamond&qid=1547955248&s=Sports+%26+Outdoors&sr=1-4

The idea is that i just go ham on those when i cant go to the gym so i dont lose strength.  If yall use these as serious trainers, let me know what you think of them.

I got the kootek ones a few months back and it has made a noticeable improvement in my pinch strength, which is what I got it for.

Trust me, spend that money on a hangboard instead.

Grip Pro Trainier rings are much better than the Black Diamond ring.

https://www.amazon.com/Grip-Trainer-Forearm-Strength-Gripper/dp/B005JPWF1I

You should also use Powerfingers as they train the antagonistic muscles/tendons to help prevent injuries. https://thepowerfingers.com/ 

sandrock wrote: Grip Pro Trainier rings are much better than the Black Diamond ring.

https://www.amazon.com/Grip-Trainer-Forearm-Strength-Gripper/dp/B005JPWF1I

You should also use Powerfingers as they train the antagonistic muscles/tendons to help prevent injuries. https://thepowerfingers.com/ 

You can get generic versions of those power fingers for under $1 on EBay

Thanks for all the suggestions!  much appreciated!

One time at Neptune's in Boulder, I dismissed the utility of those finger trainers by making a jerk off motion and stating "That's probably more effective training than these" or something like that. I found out years later that it offended her.