I'd say a con - I think the 'selling point' is that it makes the butt lighter (?), but how much does 6 inches of neoprene tubing weigh?
I find them uncomfortable to use, as I often reach for, or grab the butt, expecting a full-length grip, but grabbing only a carbon tube...
I'm there will be other opinions/justifications, but I'd say it's nothing more than a way for tackle companies to sell a few more rods - "It's different, so I've gotta have one!"
There's one born every minute, as the saying goes!
Cheers,
Mike.