Advice and help on Ben wa/kegel balls

So I've been wanting to try out some sort of ben wa/kegel balls for quite a while.
Though I've done a fair bit of research I thought I would come on here and ask for advice and tips as if completely new to the idea, that way the post is good for those who do and do not know about them aswell as me making a better decision on what I would like.

Eg:
What is recommend for a beginner
What is better for toning
String or no string
How to use them for toning and tightening
Removal of those not on a string.

~x~