Will it fit my 79cc Predator go-kart engine?

Yes. It is listed for the 79cc 3.0 hp Predator engine used on go-karts and mini bikes. Check your engine displacement before ordering, since larger Predator engines use different carburetors.

Does it fit Honda or Yamaha small engines?

It is listed as a replacement for the Honda and Yamaha IE45, 152F and 154F gasoline engines. Those engines appear on generators, roto-tillers and other small equipment.

Do I need to tune it after installing?

Expect to set the idle speed and mixture after fitting. Generic carburetors often run slightly rich or lean out of the box, so a small adjustment is normal.

Are gaskets included?

The listing does not state what comes in the box. Reuse your old gaskets only if they are intact, or have a gasket set on hand before you start.

Is this a good upgrade over the factory carburetor?

It is a replacement, not a performance upgrade. It makes sense when the original carb is worn, clogged or running badly and a rebuild is not worth the effort.