I would say Quantity is a big factor in how strung out you decide get on making bending dies, for a couple of pieces sand would probably do........If you have allot you should forget about sand.
The prefered method in the photo is done primarily with a machined die (in ctr of the diacro, hossfield etc)and will usually do the pipe in one sweep without distorting the sides, cold.....The machined die doesn't have to be in a bending tool to work, you simply pull the pipe round by hand......hot I would reckon
A simple thing to fab shown in the drawing is a jury rigged version of the machined die made of round pieces. It will work but is more hassle cause the expanding sides of the pipe will pinch, when you feel that happening you need to slip it out and tap the swell into shape before you resume bending.........mb