Can I get your opinion on Black Sumatras? I have a chance to buy a pair of 4 month olds. I have read places that they are aggressive, and not happy being "coop" up. I do let them free range about every other day and they would be in a large yard(20x16) with about 20 other birds(BR, RIR, and some mixed breeds) Does anyone have any opinions on them? Thanks in advance.