First thing I checked for! I feel like it's such a niche feature but also distinctive. It's actually a "necessity" for a proper Gamecube emulation experience, which has the two stage shoulder buttons.

Like you, I also used this for boost on Rocket League and it was surprisingly intuitive. You can map it to the triggers lowest threshold to emulate it but without the tactile bump to rest against it just won't work.

According to digital foundry it does have dual stage triggers

Praise Gaben. That's the one thing I've needed in any replacement Steam Controller and Valve finally did it before the last of my OG Controllers gave up the ghost.

I think the person you’re replying to has made a mistake: I looked extensively last night and there’s no mention of the Steam Controller having dual stage triggers.

However, the Steam Frame Controllers do. Seems weird they would add them on the Frame wands but not the actual controller replacing the controller that does have them.