On average, they're about 10 bucks more than a comparably sized KB at a good place like dragondoor.
For people in kettlebell competitions, I guess it's a cool way to add a little flava. I wouldn't do it, but then I also wouldn't get some custom bowling ball.
I might feel differently if I competed in either sport (sport?).
For the average trainee, If it makes you feel like a badass when you're training, it's no different than wearing your favorite lifting shirt, under armor, etc. It costs a bit of extra money but makes you feel cool.
Thumbs up from me. Enjoy your demonbells.