The one I got (details in the thread KylePa posted) is holding up and working well but the scions need to be well matched to the rootstock in diameter and in the right size range. I'm getting at least as good results with it as I get doing W&T with a grafting knife (but I'm not expert at W&T). It is much faster for me. A knife (in the right hands) give you a lot more flexibility with things don't match. The tool I have is much faster for me when the diameters are in the range of the tool and well matched.
One note: If you look at my post in KylePa's link it has a link to another forum. These cheap tools (like mine) are Chinese knock-offs. Several folks have reported broken tools and such. QC is pretty much non-existent. So, you pay your $20, spin the wheel, and see what you get. Mine are several seasons old and are doing fine.
Thanks,
Jack