They have exclusive rights through Elon Musk to tesla's battery and other technologies that will eliminate the need for net metering. (You will charge a battery at night that could be used to completely break off from the grid if you wanted, or you don't need to give out electricity during the day and take it back off the grid at night and pay a net metering fee if there is one.) Basically their whole solar panel system, can not be competed with. People trust that the Solar City brand will install this system the safest and most efficiently.
That is the investment pitch I would use. Also they are leveraged perfectly for the solar market because if solar demand goes up they make money from more installations, and if solar demand goes down, panel prices will drop and they can lower their prices as well. Can't really lose economically with SCTY.
Look up partnership between PowerOne (now owned by ABB) and Panasonic. PowerOne is introducing a home-power storage solution using Panasonic batteries (ie. same as Tesla) which is exactly as you describe. No uniqueness to SCTY solution and overpriced if carrying the TSLA label on the box.
Going off the grid will be hard to do if you have an EV. The size of the solar array and battery system will be very cost prohibitive for most people - only the top earners can afford such a setup. Forget the lease - buy it so the house is easier to sell if you move. The lease with the lock-in of 2.9% is a strong-arm tactic when American electric prices are flat and staying there (except California which has its own problems).