As a newbie - without information like this forum - I was sold a DaKine 'Surf Seat' last Fall. It's really comfortable and converts from seat to waist harness...is styled well...but it has a few short commings - like some crap construction.
After the third wearing, I had to re-sew the leg straps. And the plastic buckle was something a product liablity lawyer would like. It's the thing that was perhaps actually dangerous about this harness.
I looked for a simple metal buckle, but none were available in Stainless. I tried a better plastic one (shown) - No Go. You could actually hear the webbing slip out.
The solution was actually simple; a double D-ring. I can pull it quite tight because I am pulling back toward the center, not away. I've even played 'Swiss mountain boy' by swinging from a tree in it to make sure it would hold well.
I'm pleased I didn't have to chuck it out. I have the advantage of having all the machines and materials, but any canvas or shoe shop could duplicate the results. ...but then you're smarter than to buy any of this shite, eh?
Have fun - be safe.