I saw what looked like nylabones given to the dogs to chew on.

I have heard these are quite bad for them.

Am i wrong?

Or are there any guidelines to buying them?

Thank you!

From what I have read the best answer would ne for a less aggressive chewer with proper supervision.  There is the chance thwt small pieces can be scraped or broken off and swallowed .  

Depends on the dog. My parents have used them for their dogs forever. Their only big chewer leaves them alone. I would NEVER give my dog one. My dog is a gulper. 

I use big skin chew bones for my dog. I can leave it in the crate and sometimes it takes him 4 days to finish one. I haven't found a better chew toy or food so far.

My dogs love Nylabones. I have begun leaving one in the crate with my puppy. Once she settles down, I will hear her happily chewing. Nylabones are great products and durable. I would just be sure to inspect all your dog's toys consistently to make sure they are safe.

Nylabones are great! They are designed to be chewed and broken into small pieces no larger than  grain of rice. Some even have flavors and the parts that are swallowed just pass through the dog. Of course its important to throw them away when there is a small portion left so its not swallowed. They are also relatively inexpensive for the cost vs duration.

My dog can't get enough of them, and she goes through bully sticks in just under an hour in her crate. 

My nylabones have held up better than any other toy I've gotten my Doberman.  I do keep an eye on her when she has one though and I don't leave her alone with one too long.