RectMask2D - What am I Missing?

So I read there's this new toy in town, RectMask2D. It's good for UI masking. Awesome.

I try it and... can't get it working. What am I missing? I read the API, mmmmkay... I do google searches, forum searches, and... what gives? I'm on Unity 5.2.2.p4 so the initial issues should be resolved but... ???

GameObject -> UI -> ScrollView
Okay, cool, insta-scroll-view. Add items to content (images, text, etc.). Works, great.
Remove RectMask. Add RectMask2D. Cannot see anything.
Disable...

RectMask2D - What am I Missing?