[Cyberdemon]

Perhaps safety is subjective - ex we survived the 1970 and 80's with only lap belts.

People have absolutely died from head/neck trauma as a result of driving without a helmet + HANS device on the street due to impact with the cage. Now you could argue that with a half cage your head shouldn't get close enough, but you also need to consider the flex of a racing bucket in the event of a serious impact and whether or not that is actually true.

More importantly, in a hard front end or rear end impact, a properly tightened harness will transfer all of the load directly to your neck. Your stock seatbelts and airbag are designed to reduce the overall impact of a collision by allowing your body to move and more gradually absorb the impact.

4 Point harnesses which is what most people choose to run have a high risk of submarining in a crash, aside from the general practicality issues like reaching (which is going to be a function of how long your arms and legs are. I can tell you that at 6'4" my seat is far enough back that would probably be an issue in most cars.

Have I done it? Absolutely, my college roommate had a spec Miata and we would regularly hoon it around on mountain roads with a full cage, 5pts and no helmets, but in hindsight it was pretty stupid and things were different when I was 20.

People do lots of things with cars that are generally not recommendable, you just need to decide if you think those risks are significant enough that you're willing to accept those risks. I would just reupholster my interior with some cool fabric for a fraction of the price and retain all the practicality of the OEM seats and belts. You aren't taking a convertible on the track, so why add racing equipment?