How do they lay ? Hard to say, as they are first generation and are just starting to get the first pullet eggs. Looking at the parent stock, on the male side decent to good layers. The cornish blood on the female side is not likely to improve it any.
Rate of maturity ? I would say regular slow as you put it, they are very hefty birds, but shorter, and faster to mature than my Brahmas.
Fertility ? I would not expect fertillity issues, while they have nice wide type, they do not have the extreme width or short leg length that tend to cause these problems in show quality Cornish.
Meat production The extra males were very large and well developed, even the hens are well muscled.
Eggs ? We will probably float an auction here once they are laying.