With a harness, there are a few things to consider.
Make sure there aren't anything that the bird can easily undo themselves. That includes metal spring clasps/hooks, velcro, etc. If a toddler can undo it, a bird can too.
Make sure there isn't anything that can dig into the bird. That includes, again, metal spring clasps/hooks.
Make sure the point of connection between the leash and the body harness can swivel. If it's attached a single point, it can (and often will) flip a bird off balance and over, rendering them unable to control any descent or recall back to you.
These three points are why I prefer an Aviator harness. It has no parts that can dig into a bird's body, it is bird proof from opening (unless they are given a ton of time to tear it apart, in which case no harness is going to survive that), and the leash is part of a swivelling waistband.
That being said, others don't like the Aviator harness because you do have to train for it.
Some folks prefer what's easier to put on without the bird getting a say. Other harnesses are easier to put on (they have all the metal/velcro parts that make the process less involved for the bird). If you don't have the time and patience to train your bird, the Aviator may not be for you. But be aware of the risks of the other harnesses out there.
That being said, our ekkie who hates being touched learned harness training within 2-3 weeks. He will literally fly over and lean forward just to shove his head through the neck loop.