Our 85 pound pitt loves the tizzi. its her new favorite. We have all of the zogoflex toys and I recommend them to everyone. I even just bought my brother's new puppy a tizzi and a hurley and he loves them. I give them as gifts all the time.
Every so often she gets a chewing bug and will sit there and gnaw on the ends of them, and yes she can and does chew through them. But the toys don't fall apart and she continues to play with them. When she swallows the pieces they come out the other end whole, so I don't worry about it hurting her.
Her first bumi we got her as a pup and it got us through her teething phase with little to no damage to our personal property. She has chewed both ends down to the thickest middle part, but she loves the thing because its harder for us to "steal" from her, we call it her stubby.
The hurley she got toward the end of her teething phase so there were a couple of tears from her dagger teeth, she has chewed part of an end off, but again it didn't fall apart and she still loves to play with it.
The huck has withstood the test of time the best, but she can't hold it down with a paw and gnaw on it.
With the tizzi she seems more interested in the ball portion of it than anything, and she loves when we stuff it with treats or peanut butter. Its a great game for her to figure out how to untwine the "legs."
I don't think any toy is perfect, for me it has more to do with how long does it last and is it worth the money. We still have every zogoflex toy we have purchased and she still plays with all of them, even if she has "altered" some of them.