Super reliable. I used to get at least 1 speeding ticket per year, I haven’t had a ticket in 8 years thanks to Waze.

Also Waze time estimates are stupidly accurately. You think you can beat their estimate by driving faster but it somehow accounts for that, eg if average speed on 101 is currently 80 mph the estimates will reflect that. Waze puts Apple Maps to shame for navigation.

The way it reports adding a stop (say for gas station) as how many minutes off route is extremely useful.

It's been fairly reliable in practice, but it's based on crowd sourcing. It'll ask you to confirm if you see one someone else has flagged. Sometimes you're the first to see it, sometimes the alert is out of date and there's no officer.