I'm a dentist, so am not keen on generic home- fitted gumshields, but this was a surprisingly effective emergency purchase for a 9 year old child (with a mixture of adult and baby molar teeth) playing soccer the next day.
It did take me 2 attempts to get it right as I didn't apply enough pressure to seat it correctly first time around- simply repeat the heating instructions- and said child wasn't happy about the heavy finger pressure needed to seat it effectively, but it fits him quite well and should suffice until I can get him a custom made one. You do need to be really sure that the gumshield is fitted well enough to ensure that it stays up on its own, or it won't protect the teeth effectively.
We are really pleased to read that you liked it and particularly so given your professional background!
We hope they enjoyed their game!