SmartBalls are both a Kegel toner and sex toy depending on how you use or "enhance" their use. Designed for vaginal insertion, a metal ball bearing inside of a sealed sphere rolls around when you move.
 
As an exerciser, the textured weighted ball engages your Kegels by (1) sending vibrating signals to your muscles and causing them to involuntarily tighten and (2) by creating a mass that your vaginal walls need to respond to by flexing and gripping. The act of resisting is what strengthens your muscles.
Whisper quiet, only you will know they are there unless you want to share your secret. Try inserting them during a night out with your lover. Wear them grocery shopping, then add a vibrator when you get home.
 
SmartBall spheres and "pull string" are coated with a hypoallergenic silicone so they'll be easy to clean and work well with any water based lube. The makers added a finger hollow to aid insertion. SmartBalls are the top of the line for quality in this category.
Uno offers a single sphere with string for removing. It's perfect for the beginner or the person who wants a little less mass, perhaps to add a penetrative vibe to the equation.
 
Colours Vary -