IMHO dual roll bars suck aesthetically - they scream "kit car!" and are the ricer wings of the Cobra world
. The original reason for the single roll bar is based on the concept of racing on sunday and driving to work monday. The only time rollover protection was needed was when hauling a$$ on the track - ie: only the driver in the car - no need for passenger protection.
On the street; the idea was that, when hauling passengers (as opposed to a$$), the responsible pilot would consider pedestrian issues like the rules of the road and the safety of their significant other. Under such circumstances, a Cobra is no more likely to suddenly turn turtle than any other convertible (yeah right) and no more needs to be festooned with multiple hoops than a stock engined Civic needs the downforce of a massive rear wing.
Having said all that, I respect that there are those faced with circumstances that transcend the triviality of aesthetics.
Wifey sez "You don't care if I die!"
Track driving instructors won't ride without one.
Folks at the show 'n' shine think your early Vette looks lopsided.
So, tell opinionated people like me to stuff it and do whatever suits you best.