Here's my honest opinion :
I have a Steve's 2 piece CF shaft with the 4" counter weight. He has a few other sizes as well. You can unscrew the cap and adjust the weights inside. He uses birdshot in small plastic baggies. With the 11" coil , I think it is a vast improvement. But with the 15", not so much. This was the primary reason why I bought it. I got rid of the birdshot and put in a heavy custom SS rod to add more weight. It worked marginally better. Maybe I should have bought the 6" so I could have added more weight.
I'm not sure it's worth the $200 I paid for it. I think more importantly it depends on your hunting style. If you only do 2-3 hour hunts , you will be fine without it. But I hunt beaches , putting in 4-6 hours , walking at least a few miles swinging away. Usually with the 15" coil. These shafts are well built , look cool , and better than the factory shaft. It will last a long time. But worth it ? Not to sure. It didn't completely balance my detector with the 15. With the 11" you will be fine.