"The more rigid the band is, the more chances you have to shoot your hand."
Can you explain this ?
According to older people this kind of slingshot was used in Macedonia at least 50 years ago (using thick rubber stripes cut from tractor inner tubes) . Probably the idea came from Asia.
Also I use one with double thera tube red (as shown above) and I have no problems - the tubes also last much much longer.
I think the only point of serious and careful consideration is the pouch (avoid thin leather and too short string).
Btw the knot you use for attaching the pouch to the rubber is not constrictor knot.
This is a constrictor knot:
The knot you use is this one :
most of the time called : Lark's head (cow hitch)