Ok, but

> // By overriding this built-in method the corners of the vibrant view (if set) will be smooth.

If you don't override the built-in method, the corners won't be smooth. Jagged corners cause thousands of eye injuries every day.

Using (or overriding) private APIs comes with risks, but sometimes it's the only way to get things done. Of course, it comes with consequences too. Sometimes vendors test their new releases with commonly use applications and reach out when they've changed things and breakage results, but testing releases isn't webscale.