Unintentionally i grew Sorghum and Amaranth in quantities last year: Those are a huge part of winter-feed for song-birds here in the U.S. and those birbs are messy eaters, so i ended up with Sorghum (aka. Millet) and Amaranth everywhere. These plants grow incredibly fast to heights of way over 2 meters (6½'), out-compete everything - even potatoes - and cast shadows on whatever you want to grow.
I want to make the best out of it and tried to harvest some bird-feed, but there were two obstacles: The wild birds who ate most of the grains before they were even fully dry and the plants themselves. You have to thrash them really hard before they release their seeds and then you spread these seeds all over the place. And pray that no strong gust of wind comes your way as these seeds are tiny.
Unless you really want to be serious with these plants, growing them in large scale (bird losses!) and have the right equipment to harvest, choose something else.