My Mannlicher Schoenauers all have them. I do remember and have seen the single trigger option that used to be available for the rifles. I always thought that looked so out of place on them!

DST's on a JP Sauer commercial Sporter 98 Mauser,.
Steyr sporter in 6.5x53R
Novatny (sp) single shot break open 50cal stalking rifle

I sold a 98 Sporter w/ DST and a Greener (side) safety. Kind of a different combination. The original bolt safety still there. I guess the Greener safe was quieter in a stand.
Rotating the Greener safe blocked the front trigger only of the DST and could be used only with the DST in the 'set' mode.

I have several sets to go into M/L rifle projects in the future. The last rifle I put a plain single trigger in for some reason. But I really do like the things.