I didn't get free bonus birds, but I did order Murray McMurray's "All Heavies" special. It sounds like this is what other compamies call "bonus birds" and give away for free. I wish I would've known that...
At any rate, I raised these dual-purpose birds while raising and butchering a couple CX batches at the same time. I totally agree with those who advise against getting these birds. My dual-purpose roosters are now about 17 weeks and have been trying to kill each other for well over a month now. Thank goodness they are located 100 yards from my house because they crow all the time. As for meat yield...they don't even compare to CXs. Their breast meat seems to be about 1/4 that of the CX. Their plucked carcass looks like the ol' gag rubber chickens in comedy sketches. The taste was fine but the behavior, time and effort doesn't seem worth it. I'm not trying this route again. I'd rather pay the extra and get CXs to get a better return on my resources. I must, however, a couple positives of the DPs. They are MUCH cleaner and more interesting for my 2-year-old son to watch.