I don't, but I use other dual purpose chickens. I don't use breeds, I selectively breed mutts.
Are you considering hatchery quality Marans, show quality Marans, or have you fund a source that breeds Marans for meat, for eggs, or both? Your starting stock can make a world of difference in how they turn out. Don't for a minute think that all Marans worldwide are identical, they are not. (I can't believe I said that to you of all people on here.)
What makes a good meat bird to you? Size, early maturity, ratio of white to dark meat, or something else? What is an acceptable egg layer? Do you eat both male and female or only male? I don't need to know any of this, just things for you to consider.
My suggestion is to raise some Marans from your source and see what you think. You are going to feed and manage them differently than I would. It's your opinion that counts, not mine. Get enough so you can see what the averages are. Typically I see some pretty small late maturing ones in the same hatch from the same flock as some really early maturing big ones. If you have enough room get another breed or two at the same time so you can compare them growing up with the same feed, management, and climate.
Don't depend on what some stranger like me says over the internet. Make your own comparisons and use your own judgment. That will fit your criteria and your growing conditions better than anything I could say.
