Touchless ID has been in use at the Terminal 1 (Gates B and C) security screening point since at least a couple months ago. Since there is a separate line for it next to regular Pre Check, you effectively get to cut to the front of the Pre Check line if there is no one in the Touchless line (which there never is IME, so far). Once your identity is verified you join the same screening stations.

How much time it saves depends on how long the regular Pre Check line is. I suppose it also saves a few additional seconds in that you don't have to fumble for a physical ID, along with whatever the added convenience is worth to you.

I don't recall specifically opting in, but I must've at some point when checking in for a flight. The airlines apparently remembered my selection, and now I'm too lazy to opt out again.

It's not yet in use at Terminal 3. Don't know about Terminal 2 or International.