You will not increase your strength by pushing the same resistances over and over again. Not in the long run anyway. Nor is it wise to start off as heavy as possible and go from there.
It is far more efficient to start off with low weight and gradually increase it until you reach a max, then unload and start increasing again until you reach a new max etc.
That's why I think that those tools you bought are not particularly efficient for the sake of increasing max strength. They may be good for warm-ups or auxiliary exercises, but should not become the main thing you do.
If you want to increase your grip strength, the some good ways are to simply pick up shit and carry it around, hang onto bars with a timer and add weight as soon as you beat a certain time (anything between 20 seconds and 1 min should work), and shit like that. Climbing and similar sports would probably also help a shitton.