Pushing on a spray can valve with your index finger can get tiring quickly. A spray gun handle with built-in trigger makes painting a RC body much more enjoyable.
The handle show above is made by Krylon and is called the Can Gun. We purchased it at our local art and craft chain for less than the price of a Tamiya paint can. Similar items can be found from Chinese sellers on the usual websites.
The handle clips onto the neck of the spray can. A plunger pushes on the spray can valve, operated by squeezing a trigger. The handle fits cans from many manufacturers, but only cans that have a small spray valve diameter.
The handle makes the painting experience much more enjoyable as it takes away the strain of having to push onto the valve from the top. This allows better concentration on the paint application, and therefore leads to better paint jobs.
If you use one can per year it is certainly not needed; but if you are sometimes painting four body shells in one session, it is a great tool to have.