I have had Metromile for 2 years now and am very happy with it. We family drives around 3,000 miles per year and it saves us a little money, not a ton.
It has some cool (and optional) features that let you see the vehicle location via the app, like if you forget where you park. You can also login and see all the trips you made which is useful for logging tax-deductible business miles.
I think the pay-per-mile model is smart and incentivizes people to drive less.