It worked well enough for me because I removed the head as soon as the guinea was dead. If you are concerned about blood draining, pithing works well and has the benefit of making plucking easier.
If you are unfamiliar with pithing, do a search for pithing in the Meat birds forum.
My father taught me to not process guineas by chopping their heads off. He claimed it would cauise their bodies to become black and blue. His method was to shoot them in the head with a .22.
Poultry are very segregated and will often shun or pick on a member that is different. It didn't happen much in my flock because so many were different colors.
I have raised them both ways, with chickens and by themselves. I will never raise them with chickens again. You think chickens can be savages, they have nothing on guineas.
The majority of people who raise them with chickens say how wonderful they are. Once the first breeding season starts...