I have heard on here that anything you cant dent with your fingernail is considered too hard to chew and can crack molars. I feel like 'safe' has a lot to do with the dog. Mines impatient so he chews hard and swallows as soon as he can. If your dog is a hard chewer/swallower you cant guarantee safety. On the other hand some dogs will chew bone/antlers their whole lives and never have a problem.
I like these: https://www.amazon.com/Earth-Animal-No-Hide-Chicken-2-Pack/dp/B0125DS0LU
Edit: oops I meant to post this as a separate comment!
As /u/sharkfacee said, it’s No Hide chews, and he (Radar)goes absolutely insane over them.
https://www.amazon.com/Earth-Animal-No-Hide-Chicken-2-Pack/dp/B0125DS0LU
you can also try no-hide https://www.amazon.com/Earth-Animal-No-Hide-Chicken-2-Pack/dp/B0125DS0LU