Has anyone used this before I wanted to buy them but I don't know if they would work the product had a review and some people said they don't work and some say they do so I want to know what you guys think? here a picture of the product . the  size aresmall ,  medium , large and x-large .

I used them years ago, and really liked them.

But, I tried them last year, and you absolutely have to use the proper size for the thickness of the eye, ring, or whatever you are clipping to them.

Too large a size, and they will not hold well.  The hook, bait or lure can and will slip out while fighting fish.

Too small a size, and it will spread the opening.  Eventually, the flexing will cause the snap to break at the horseshoe bend.

Unless everything you are "snapping" onto your line has the same gauge wire, you are better off retying.

One thing about retying, every time you do, you recheck the line for nicks and other damage.  

You should always check for damage after every fish or hang on the bottom that you manage to work free.

Depending on the structure and cover, you may need to cut and retie so much that the fast snap will not be much of a time saver.

Plus, every additional piece of equipment between you and the fish is one more thing that can fail.

They would probably work fine for pan fishing, but not so well for game fish.