The SG has a very tiny cup. Actually it shouldn't be called a cup, more of an indentation in the body. Unless you like refilling airbrushes...
The side feed is just that. A side feed brush. The color cup enters the body at the side. It still requires some siphon effect to work, as the bottom of the cup extends below the body of the airbrush. But because it's a side feed, it doesn't have to pull the paint straight up. If a top mounted cup requires 12-15 psi and a "true" siphon requires 15-20 psi, the side feed would be in the 13-17 psi range. For $26 it's a very nice airbrush. I'm considering one for my collection.
The neat thing about the side feed is that you get the sight line of a siphon, without the cup extending so far down it interferes. You can also rotate the cup so you can paint straight down. That was a feature for photo retouchers, but would come in handy!
And yes RH has the cup on the left side of the body for righties, and the LH is on the right for the south paws.