Companion offers additional story but come with forced choice you must make or suffer attitude issues. That's all. Stat-wise, they just come with a preset you can choose when you recruit them and when you finish act 1, you can respec them all you want.
You can chose and change them on act 1. At the start of act 2, you select the final 3 that will stick with you until they hate you enough that they leave you. It's best you decide who you really love and stick with them since act 1 so you can do their story quests and improve the relationship.
Playing as the companion is required if you get to see some of the dialogues that get hidden by the narrator though but that mean you can't make your own char to go to bed with them.
Also Red prince is the best and should be in every team for his personality and looks.
