McDonald's signed an agreement making BM their preferred supplier of fake beef, so Impossible is put at a disadvantage. Absolutely none of this replaces any real beef with fake beef, or even results in less real beef eaten or sold.
Beyond meat makes basic veggie burgers. There's nothing special about them you couldn't make without the recipe.
Impossible foods has the yeast sourced heme thats supposed to make it taste and cook more like meat. That's patented, and not easy to replace.
So BM can be in every McDonalds for a year and then be replaced by a McFakeMeat Burger and there's nothing they can do. Impossible actually has a product you can't make.
In the long run I think Impossible is better food. The question is always one of price.
I also think there is a good chance MCD will announce their own fake beef product in the future. At least that's what I'd do if I were them -- they probably know a lot more about food science and also know their requirements well.
I've tried Burger King's Double Whopper and Impossible Whopper side by side, and even though the Impossible doesn't taste like real meat, I was surprised how good it tasted. So much so that I would have no problem forgoing real beef and going with the Impossible Whopper. (I have since returned to BK many times and have just gotten the Impossible Whopper)
Beyond doesn't inspire that kind of reaction. It's just like any old veggie burger.