I replaced the bearings on my Specialized Allez Sprint. They were internal BB30 bearings and still seemed to spin but also had slop back and forth from the beginning of the life of the bike. I debated having the shop put in a new set for me and pay them a fee or buy this and do it myself.
I'm so glad I bought this instead. Not only was the install super easy, my crank is rock solid with no slop or play. I can feel the snap of the bike when I put the power down. When using the trainer, it's as smooth as butter.
The only drawback is the added weight of the shell. Honestly the benefits out weigh the grams!
If you're on the fence about this product, don't hesitate. You'll be glad you bought it.