I have two boys - 3 and 5 - who share a bath. The crackling bath crystals caused a lot of interest and a surprising amount of noise.
Sharing one packet between two children meant the whole event was over in about 30 seconds. However, left to their own devices I suspect the packet would've lasted 2 seconds as it would have been poured into the bath in one go.
Both boys suffer from mild eczema and I can report that neither suffered any flair ups as a result of using this product (although as always it should be patch tested if your child has any serious skin problems).
As a once off treat, this is a fun product. It is worth mentioning that neither have asked for a crackling bath again, whereas they love, love, love the colored bath tablets (also by tinti) and keep asking for more.