The engineering mob i got the flat bent at had some 90 deg elbows handy. They were prob 1-2mm wall thickness. Id say they were exhaust pipe but mandrel bent as there were no squashed section on the inner radius.
If this guy didnt have these i was going to use the heavier pipe fitting which you have seen. If you do get the heavier ones, get them with the chamfered edge (weldable). It makes it a lot easier to weld.
Mine were very heavy in the end.

