Depends where you live Wendy,
If you are in the UK it's probably not a good idea to drive the curtosy car on your own insurance.
Not that the service company will let you, the cover your own Insurance would provide at best would be only Third party fire and Theft. So saying if you were in an accident that was your fault and the car was a write off you get to but the Service company a new car.
If you call your insurance company in advance they would probably give you a temporary cover note for the Service vehicle at a cost.
My question would be why bother ?
The service company already think you are an acceptable risk or you wouldn't get their car in the firstplace !