>>9588233You can use google to find out what the differences are.
Main point: siphon needs a jar of paint to suck from, gravity can start spraying with one drop. Most of the time you don't need to spray a lot of paint in this hobby.
>>9588237Never say never. If you have to spray a lot of the same color on a large-scale model, siphon could be useful if you already have it. It's just that truly large-scale jobs are too rare to justify buying it.