I read too somewhere that they can't close their mouths, but I have a 6-7" BP and believe me, it can bite if it wants to. Mine has actually made me bleed a few times while I clean the tank (really minor bites...they have small teeth). He's fairly aggressive too...he picked on my blue gourami and it died of stress.
I have him with an angelfish, two clown loaches, and a bala shark in a 55 gal (I'm going to upgrade to a 123 gal wide tank because the clowns are getting big). Blood parrots shouldn't have many problems as far as tankmates, just don't keep them with big, highly aggressive fish, but don't keep them with really delicate fish either. Tetras (bigger ones, they can inhale neons and other small ones), loaches, and other dither fish will work well with them.
Also, they will eat almost anything. Mine has eaten guppies, frozen foods (like brine shrimp, blood worms, etc.), flakes, and pellets. He's even eaten an algae wafer before. When I kept zebra danios in there, he somehow ate them all...I thought they would be too fast for him to get.
They have alot of personality too, like almost every cichlid. Mine comes to the front of the tank to greet me whenever I walk past the aquarium. And don't feed them, no matter how hungry they look.
Anyways, good luck if you decide to get one!