The car insurance available from Tesla for me, a California driver, was not ready for prime time for two reasons: (1) It lacks written coverage for "permissive use", and (2) it was not really cheaper. For both these reasons, either one of which would have been sufficient, I have canceled my Tesla policy and gone back to what I had regarded as the hideously expensive Mercury policy.
(1) Normal California insurance companies such as Mercury include coverage for you and your car no matter who is driving it so long as they are driving with your permission. The words of my Mercury policy, which is standard, reads
"Persons Insured: The following are insured ... [for] the owned automobile: ... the named insured and any relative, ... persons listed as drivers in the policy declarations, ... and [the permissive use section] any other person using an owned automobile, provided it is used with the permission of the named insured, express or implied, and within the scope of such permission, and persons residing with such permissive user and related to such permissive user by blood, marriage or adoption, including wards and foster children..."
The Tesla policy includes no provision for permissive use. I asked the Tesla rep about this, and he said that of course the Tesla insurance would cover occasional drivers who drive the car no more that twice a month. But he said that he could not put this coverage in writing, and that maybe by the time my Tesla policy (now cancelled) was renewed, they would add coverage for permissive use to the written policy.
(2) For me as the sole driver, the Tesla policy was much cheaper, about 60% of the cost of my former and now again current Mercury policy, with identical coverage limits. However, when I added my wife to the Tesla policy, it became about 110% of the cost with Mercury, which covers both of us as drivers. While my wife almost never drives the Tesla, if she were to do so and have an accident, I don't know how we could be certain that the Tesla policy would pay off if she had not been listed as a covered driver. Even if we were to rely on the verbal assurance from the Tesla insurance agent, how could we establish that she had not pulled it out of the driveway 3 times in the past month and thereby have become ineligible for coverage even under that assurance?
Maybe others have worse non-Tesla policies than we, as older, extremely safe drivers without tickets or accidents, have; so that the Tesla policy might be cheaper for them. But the lack of coverage for permissive use does, I think, make the Tesla policy unacceptable for most people.