Tim from the Killi club had them and use to sell them. They worked but not too well and as Alan mentioned, will only feed one tank at a time.
Interestingly enough, he wasnt using them on any of my visits to his fish room
I thought of using a few myself but stayed away from the idea because of 2 reasons, firstly, I think its better to feed small feeds a few times a day (or as Im doing now once a day) so that fry are a bit peckish and will eat more when food is there in bulk so to speak and secondly because I know it would only be a matter of time before I damaged them through turning around and hitting them accidently