Thanks for writing with your questions and concerns. The Waffle Ball is not a soft "gummy plastic"; it is hard and sturdy, and does not appear to be brittle.
(For comparisons, this is what I would picture as soft or gummy: http://makeyourownbirdtoys.com/Rainbow-Balls_p_114.html . And this is an example of a more brittle plastic ball: http://makeyourownbirdtoys.com/Kaleidoball_p_112.html )
We have used the Waffle Balls for several years on our own toy designs. We would recommend them for medium to large birds, probably not extra large birds or really strong chewers.
As with all new toys, it's a good idea to observe your bird whenever you try a new item to make sure they play with it in a safe manner.
Please let us know if we can be of further assistance.