I have owned labs in the past and after my last chocolate, Paco, died, I did a lot of research and ended up getting a Griff. Like many here have pointed out, make sure you're getting a VHD bred for hunting! My Griff, Steve, came from a long line of hunters and his dad was a NAVHDA VC Champion, so I knew he had pretty good odds.
Griffs, like many dogs, can vary in weight. I wanted a large one due to the extreme cold we get here in Idaho. Steve is now 80lbs, so he's pretty big for the breed. Many are 60 - 70.
My main decision to get a versatile breed was because I spend a lot of time both waterfowling and upland hunting. Seldom do I go duck hunting without chasing roosters, huns, quail or chukar on the drive home. I figured versatile breeds like the Griffon would make good retrievers, but probably not lab-caliber.
Boy was I wrong.
Steve simply out performs any lab I've ever owned. Their drive is unstoppable, they are extremely intelligent and their nose is like nothing I've ever seen. Steve holds, retrieves and handles very well, has a soft mouth and actually endures cold temperatures better than any lab I've ever had. Back to the nose: It's quite evident that these dogs use their nose more than most retrievers. When Steve is out on retrieve, he holds his head high while swimming, scanning above the ripples but also honing in on scent. He's three and he's already had several "head dunks" on submerged birds and birds under banks. He will stay out on retrieve until I call him back...they are beyond driven. In short, I couldn't be happier because I get all this, then get to watch him track and point upland birds like a GSP. No more worrying about keeping a dog in range. I just let him out and literally follow him around fields, etc. If he finds a bird 200 yards out, he'll simply point it and hold until I get there.
That all said, be aware of the following: These are high energy dogs. Steve needs to work or exercise every day. They are prone to separation anxiety--Steve is actually perfectly fine if we leave him at home, but if he can see us working in the yard, etc., while he's inside, he'll go ape crap barking and whining. They simply want to be with you all of the time. They can be protective of their people: Steve has a ferocious bark and is an excellent watch dog but he never bites or mouths. He can be intimidating to people who don't know him or whom he doesn't know. And they can be stubborn. He took a little longer to house break, etc. Finally, they are one of the most affectionate dogs you've ever met. My GF loves him like a child as he loves to be hugged, cuddled, etc. and LOVES his people.
Do NOT even consider a Griff as a kennel dog. It simply won't work--they need interaction and a kennel situation would be a disaster.