It will be a good supplement when used with a balanced diet. I usually mix it in water and then mix feed in. I use it about 2 to 3 times a week when I have a weak chick.
It takes a while to get them over a vitamin deficiency. I think you are doing a great job.
You can get Purina Flock Raiser from tractor supply. I believe it has 18% protein.
It doesn't have sufficient calcium for layers so you'll need to buy some oyster shell also. You can keep the oyster shell in a seperate dish.
I'm a fan of liquid Poultry Cell (also available at tractor supply)...