Literally last night I bought a used Brey-Krause harness bar + harnesses with the idea of being able to still use the rear seat for the kids since I think you can easily remove the center section of the bar when not in use. I haven't installed yet but do you guys think it will have some of the potential danger to rear occupants you describe? See pict. Thanks

 

Its ok but, the kids have to wear helmets

I had the Porsche Tech roll "hoop" like you pictured but its level
of protection is limited by its design. It is hard to have things both ways
(use your back seats, even for luggage AND have good rollover protection).That is why Luis Ruf's integrated roll cage is the best thing ever.