david_42 said:
I don't think they'll be a problem, but all they are is a noise-maker. I don't think I would want to listen to them for the entire boil.
Are they just noise makers? If they are going to make noise, then they must be buoyant enough to move around in boiling liquid, and if they can do that, they will almost certainly move toward hot spots (where the liquid will rise fastest). Having reached a hot spot, they will surely interfere with the transfer of heat through that hot spot, by diffusing the localized temperature gradient over the surface area of the disk which is larger than the hot spot.
This would in effect reduce some boil-overs, which are commonly caused by applying excessive heat at the edge of a pot, causing the liquid in contact with the edge to boil, while the liquid in the center of the pot does not.
This is almost certainly the idea behind these devices, but was the idea invented by an engineer who knew what (s)he was doing, or by a marketing person who identified something they could make money out of. Then you have to consider, did the engineer make a mistake, or the marketing person make a correct guess entirely by accident?
I don't know the answers to these questions, and if you're still reading, then you probably need to get a life.
What I can say, is that I would never use one of these devices because it is a well known fact that a watched pot never boils.
-a.
