the cage doesn't come back painted, only fitted. the quality of the install is down to the cage and not me either as I haven't bent the cage, the welds will be good and it will be square in the car.
car will need to be stripped as much as possible to avoid any extra cost in labour.

As far as anyone having a go a fitting a weld in cage, yes it could be done but if done wrong you will come off worst in an accident than if you didn't have a cage so just think back to reasons for wanting a cage.