I don't know from personal experience but I've read somewhere that they are not prolific layers but do make good mothers when they go broody.
Standard Dominiques are what I'd call "sporadic layers". Some will lay well while others will not and seems they will lay for a while then take a break all of a sudden. I Only have recently gotten Dom bantams and plan to get a few more. My grandfather use to have standard Doms and this is where I got my info. on the standards. The Dom lost popularity partly due to being less of a layer than Barred Rocks, RIR's and a few others and because they were somewhat smaller which meant less of a meat bird. I am interested in them because they are a heritage breed.
They aren't as good of a layer as some other dual purpose breeds, but they will lay whenever they feel like it, winter, summer, fall, whatever they want to do they do.
My standard Dominiques are pretty steady layers, and they started early, at about 18 weeks. Large brown eggs. I myself have no complaints, but then I'm not in the egg business so whatever I get is fine with me, I don't stress if I don't get a quota.