We had one seat and it was in my car, as we use my car for all our outings/trips as well, but we have just purchased a second seat as a spare, we will be putting it in DH's car, but it can then also be transferred to grandparents/other cars. We are also planning more children so thought it was worth the investment,, but got the second seat second hand, it was in excellent condition though.

We have the Safe and Sound Meridian in my car and we just bought the Safe and Soud Compaq Deluxe, both are reversible to 12kg (which for us was very important). Now we just have to get the anchor point for the second seat in DH's car