When brassicas first hit the food plot market, the first testing of them in TN was on my place. I planted dozens of varieties in test strips running across each plot. It was amazing to see how deer would progress through different sub-species. They would hammer just one strip for a week, bypassing all the others. Then a week laer they would switch to a different species. The problem was, no species would interest them for long. To produce a food plot that was attractive over the whole fall/winter would have required a mix of 20 different species.
Once the final mixtures came out for sale, I used them. They saw some use - some very intense use - but only for short periods. Eventually I moved away from brassicas for this reason. Other cheaper, easier to grow mixtures saw heavy use all season.