It fits my very small hands!
My hands are tiny - I've probably only met one other adult with such small hands in my life, so I thought I could give a report on the fit of the new controller for small hands.
Hand measurements: ~15.5cm palm length, 18cm span
I can use a standard XBox controller, but my main controller is/was the PowerA Nano, which is smaller. I have a Steam Deck which is usable for casual games but the triggers are a bit hard to reach, so games where the fingers must rest at the triggers to be ready at all times are kind of awkward and the back buttons are also at a strange angle that makes them hard to press, even though my fingers are technically on them.
My Steam controller arrived yesterday and I'm glad to say it fits much better than the Deck and about as well as an average XBox controller. I can leave my hands in a position where all fingers rest on all buttons relatively comfortably. The joysticks need a slight stretch when moved to the far inner edge, which is a bit uncomfortable in the longer term, but I can just use them by touching only the outer edge of the stick which negates that somewhat. In general, all the controls are of high enough quality that they are quite smooth and forgiving in terms of activation angle, which I believe helps a lot in supporting hands of different sizes.