Greenies are OK treats, some dogs like them, some dogs don't. Lennon used to love them, then for some reason he does not care for them any more.
However, there are some words of caution when using those. Given their hard nature, it's better to keep an eye on your doggie while you feed them one of these. On the OES forum I also post, we've had our share of nasty experiences with them. One of the dogs did not chew it, but swalloed it and ended up with an intestinal blockage
There's a very graphic account of the procedure
here . (VERY GRAPHIC!)
I'm not trying to bash greenies, I used to love watch my dog chew on them since he's been little and I've never had negative experiences with them, just keep an eye on your dogs while they enjoy their treat.