Nutritional yeast has more nutrition, brewers yeast is byproduct from alcohol production. Sipliment at 1 T per cup. Durvet b complex is much more concentrated and can be put in water with a little common sense. Dosage varies by weight but A 3 week old pekin needs 9 mg a day and 1 ml of durvet...
I am currently putting b complex n my ducklings water. They drink it just fine, but its easy to miss a duck unless its in all their water all day long. With 14 ducks its pretty difficult to dose each one every day but if i had just a few i would put it over a small portion of feed and dose...