The UView tool was designed to fit all cooling systems WITHOUT any expensive adaptors required.
Does it fit all of them? With the way GM caps are designed, I doubt that Cone would seal Expansion/Degas tank. Granted some of them have a vent hose you can pinch off....But not all. The last shop I was employed at had a refiller that was similar to the one in the link you posted, It leaked more often than not forcing the mechanic to fiddle with it.
Like I said, Pro mechanics have adapters making the Snap-on design an advantage to the very people their tools are designed for. I'll never understand why Snap-on Tool threads attract negative comments from people that don't even wrench for a living & more than likely have ZERO experience to base their comments on OTHER than the price.
Sure....Some of their stuff is way overpriced for what it is, That's why I have tools from 40+ different manufactures, Not just Snap-on.