I love kitchen gadgets. Whenever I see one that intrigues me, I usually purchase it. In this case, I bought the Mayoknife at my local kitchen shop.
This is basically a plastic knife that resembles a spatula. It is fairly flat to ease in spreading mayo or butter. It has an indentation along the top that sit right on top of your mayo jar.
It is a clever idea, but for the most part, a useless gadget. With the new designs of mayo jars, you really have no need to rest a knife on top of jar. A regular knife or even a spatula will work equally as well as this knife, in my opinion.
I have also found that the knife doesn't hold up really well to the dishwasher, even though, it is supposed to be top shelf dishwasher safe. It seems to "melt" slightly in the dishwasher, so now I just hand wash it on the rare occassion I use it.
I can't say I recommend this gadget. I wouldn't buy it again if I had it to do over.