The shoulder rig can be as safe as any other holster, it all depends on your drawstroke.

Sweeping the muzzle around horizontally in an arc? Bad idea.
Not only do you cover yourself with the muzzle but anyone within that 180 degree arc.
Plus the difficulty of stopping on target.

Instead, drop the muzzle nearly straight down as soon as it clears leather, continue the arc forward and up, you don’t cover anyone or yourself and its faster.

Will see if I can find a video on this.