I picked my 2 Cal Greys up at a feed store locally (Coastal), so I can't say as to which hatchery they came from. I have heard Privett has lines from the original Dryden birds, which would be a good thing. (I live in the region where the original lines were created on OSU campus).
I can say I have been very, very impressed with production, temperament, and longevity. Much less flighty than Leghorns. More productive than Barred Rocks.
I purchased them as chicks January 2015, and placed them under a broody hen who had hatched just one chick to keep that one company. They took to fostering well (after replacing one chick who wandered away).
Sadly I lost one hen to a raccoon this winter (why is it always your best layers????), so I just have the one left.
She is still laying strong going on now to 2 1/2 years of age. I know as she is my only white layer, so its pretty obvious when she's not laying.
She actually has become quite endearing coming to greet me. Both were very pleasant birds. Their genetics were good as I used them under my Barnevelder rooster and they produced black sex links for me. I still have a daughter that is a nice layer of tinted eggs (Barney adding some brown) from that Cal Grey/Barney match.
I'm keeping my Cal Grey girl for more BSL's, and next spring will likely pick up some more.
I've had excellent luck with the two I've had.
LofMc
EDITED to add: I don't know that I'd call them a true dual purpose bird, at least mine. They are lighter than a Barred Rock, more like the Leghorn body type without the crazy comb or plumy tail. You'd get some meat, but not really the quantity of a true dual purpose like an Orpington (poor layers in my experience) or a Buckeye (honestly a good dual purpose choice).