Using a
BUTTON as a handle has imo the advantages of
a.) A comfortable way of holding the Poi that allows an easy change of the way you hold the Poi (Some exampleas for different grips can be found
HERE)
b.) Useful for catches since you "just" have to catch the chain/string between the fingers and the Handle will slip automatically back into your hand
c.) According to my experience the easiest way to connect Poys to a Meteor and back while spinning. The two buttons on strings work like hooks

(A Thread discussing the connection of Poi to Meteor can be found
HERE)
d.) They are normally quite cheap and last forever (Example for a
USED LONDON DESIGN)
I dont wanna say too much - try it and find out for yourself

cheers
andy