No MX5 rollbar has been subjected to rigourous testing; yeah, there is a video of someone uptipping a rollbar, but thats not a proper test… There is no evidence that the GC Fabrications rollbar is “safer” (define safer) than any other rollbar available.
If its about safety, then your answer is a full FIA-style cage, but that will severely restrict how you use the car for 90% of the time. In normal driving, you are more likely to be t-boned, or hit from the rear, than rolling over the car. Both of which may result in that rollbar moving closer to your (unprotected) head. The bars with crossbracing, in my view, restrict use of the rear view mirror too much, and thus affect my ability to operate the car on public roads.
Plus fitment of the rollbar is also important. A welded in rollbar is safer than a bolt in bar. A badly bolted in roll bar is less safe than a properly bolted in rollbar.
Look carefull at this rolled Mustang. See the rollbar that’s punched through the floor?
Unless your friend is a professional in the field, ignore your friend.