I have only had these for 3 days now, but I thought I would my share opinion on them for anyone that is thinking of buying this product. I will do a follow up review later at some point if I change my mind on them.
Firstly I'm kind of gutted that amazon reduced the price by a quid a day after I ordered them. You do get what you pay for, I mean they are only £4 now so don't expect anything amazing. Even so, they are relatively effective, as far as I can tell so far, at toning up your forearms and strengthening your grip. A problem would be that they are slightly uncomfortable to use, and get some getting use to. Although, this may be exaggerated slightly in that I don't have very big hands. They are useful because the hand grips add a bit of variety to my workout, especially since I play racket sports and need a strong forearm.
There are better hand grips on the market, but the york one's are cheap and relatively effective. The only problems I can foresee are that the resistance in the grips may weaken over time and the actual grips on them is already slightly discoloured.
Hope this was useful.