Strengthens Core & Midsection
Tones Waist, Hips & Thighs
Improves Balance & Coordination
Fun, & Easy Way to Train
Sports Specific for Snowboarders &
Surfers

This guy at PlanetMeathead does a great review of this product so, I'll let him explain this one to you

The Worlds Best Dumbells
Saves Time, Space, & Money.
Have an Entire Rack of
Dumbells In One Pair.
Heaviest, Most Compact
Quick Change Dumbells.
Perfectly Balanced.
Comfortable Handles.
Expand Up to 130lbs.

Used by professional weightlifters, IFBB pros, and personal trainers all over the world. 
Increase muscle and strength by instantly increasing your weight loads.
A must have for athletes, and heavy lifters.  My clients love these.
When they try them once, they can't believe the immediate, noticeable
difference in strength and want a pair of their own.
As an added bonus you'll keep your hands callus free.