Honestly, I've never gotten the "diaper butt" comment in the pitch for the velcro hakama.
But, what I like about it is that it's designed so the waistband is at least as adjustable as the traditional hakama, but it doesn't rely on your belt to stay up while you're putting it on. You don't need to wear a belt while wearing this hakama.
The other thing I like is that once you have it adjusted to your liking, you can take it off just by opening one side in front, so the next time you put it on you just slide it and close up that side. Really fast.
But I insisted on getting a traditional hakama when I got my shodan because, well, it's TRADITION, darn it.
I'm saving my pennies to abandon tradition now.