It's obviously ready and safe enough for Waymo to roll it out (and they've been a lot more conservative than Uber here).
As for safety, all we really need is for them to be safer than the average human driver.
As evinced by the ~40,000 road deaths every year in the US, that's really a pretty low bar. I'd even argue that full autonomous is/will be less risky than halfway houses like Tesla Autopilot where neither side is really in full control, but that's another story.
