Anyone used those potty training 'ping pong' balls?

[sheeplikessleep]

DS1 is 2.8 and can wee on demand in his nappy, but won't consider the toilet or potty.
I thought I might try these, with him standing up and a stool (pardon the pun ) and see whether we have any more success.

Just wondered if others had tried and what you thought if you had.

Thanks