Unfortunately I don't understand French, so I can't read what's in the picture or the description. From the image it looks like it's a collection of seeds and grains, which in the US would be called "scratch" and is meant as a treat, to be given in small amounts, not as their main feed. The main poultry feed is ground and sold either as crumbles, or as pellets. That's because some of its ingredients, especially the protein and the vitamin supplements, do not come in whole grain form, and need to be incorporated somehow. Also, the crumble/pellet format of ground ingredients ensures that they are all mixed together evenly, and the chickens eat all of them. With a collection of seeds/grains like in your picture, the chickens can easily pick and choose their favorites and leave other elements behind, thus ending up with an imbalanced diet. Like if you dumped a bunch of healthy foods and candies in front of a child and let them pick, they'd likely pick out the candy and leave the vegetables behind! Unlike children, chickens can't be taught the importance of a balanced diet, so they will continue eating whatever they like best as opposed to what's best for them. The argument that "animals know best" is overrated - maybe wild animals in nature do, but domestic animals are too human-dependent and over-satisfied to be able to make good decisions without being tempted. Just look at all the obese pets who can't control themselves in the presence of treats even if they have healthy food in their bowl...
My advice would be to find a ground poultry feed where you can't visually discern the different ingredients, to make sure that the chickens eat everything evenly without picking some things out and leaving the rest.