A wide 5 pt. rollbar is far safer in a potential roll over than any low 3 pt. rollbar as is thought of as standard (Most are just too low to be of much help). The double rollbar can be designed, built and installed for just a little but more than a single, it's just the economy of safety that comes into play there.
Sadly some of us have had car's upside down, mine was a Gymkana racer; a 2CV Renault with a twin cam and Gordini transmission. It also had a 6 point roll cage and the roll over was slow enough that the car was righted and I finished the races for that day and the roof was replaced later and I was back before I lost any points in the season.
The only change I'd make to this all business rollbar is a forward braced (FIA Style)support bar into the side of the passenger compartment.