You've missed the point entirely
A proper rollcage will be fitted and mounted in way to becomes part of the vehicle - a show cage is just there for show and gives you comthing else for you to polish apart from your tailpipe(s)
Say you're car is in an accident - be it chucking the car at the nearest lampost or being hit by sombody else (ie innocent party) that show cage will have have nowhere near the integrity as a proper cage to the extent it might desintergrate and impale the occupants.
Put simply if your going fit somthing like that it may as well be the real deal.
Motorsport application or not, just commen sense really.