.. Like ScubaBB stated an adjustment is advised at some point during the dive. I don't believe any buckle or belt will compensate from the surface to 100+' at some point you need to "hitch it a bit". .
Well if you have NEVER used this piece of equipment, then you might be surprised that you DO NOT have to screw with the belt buckle on a rubber, elastic weight belt during the dive. It has sufficient elasticity for every suit I have worn (including a 7 mm FJ, 7 mm jacket and 3 mm vest set up) WITHOUT touching the buckle during the dive.
As for BB's comments, s/he seems to be implying that a diver who chooses to use a rubber belt does not have sufficient "skill" to adjust a non depth compensating belt during a dive.
That is a nonsensical assumption, but I do like the skepticism that people are expressing about them. If you can use a piece of gear that is "set-it and-forget it" before a dive, why wouldn't you want to use it? Cinching up a nylon belt super tight before the descent is uncomfortable and may impede breathing and definitely makes it more likely that the belt buckle will fail and the belt could be lost.
A rubber belt can be worn very low on the hips and it tends to have more friction than a nylon belt, so it will be much less likely to rotate, slide around, shift or require any adjustment.
In addition, because the belt is elastic and stays where you put it, you can wear it very low on your butt in a location where a nylon belt would just slide off. For people with low back issues, being able to take the weight off the small of the back can make a big improvement in comfort.
The skeptic must be wondering, if these belts are so much better, then why are they not often used by scuba divers? Surely if there is something as simple and inexpensive as a weight belt that could be drastically improved, it would already be in common use?
Well, I can't answer that question... But if you are curious, you should try one.
Also, skeptics should understand that it would be VERY unusual for a serious freediver to use anything OTHER than a rubber belt, particularly if they are wearing a (compressible) wet suit.