I built the MovieMaker tool for the original Company of Heroes. The key goals were to seamlessly blend cinematics with gameplay and to reuse assets that were already created for the game.
I haven't used Source Filmmaker but I wouldn't recommend using the MovieMaker tool for actual films. The use case is completely different.
I just want to say congratz on being part of making a great game. The opening level with the Normandy landing where the cinematics led into the level was amazing. I remember feeling terrible giving the orders for the soldiers to move out of cover to take the machine gun nests knowing that half of them would die in order to advance. It was both disturbing and awe inspiring at the same time. A pretty amazing game.
I haven't used Source Filmmaker but I wouldn't recommend using the MovieMaker tool for actual films. The use case is completely different.