A friend bought 3 sets of these (six grannies in total) as a novelty gift for his gran a while ago and we all expected them to be a good few hours of fun.
This was not the case however as they worked for a few minutes then one unexpectedly broke, we carried on then another one went and in the end only two were left working out of six.
These look like they could be a very fun product to have but be warned they look like they have a tendency to break...