It is efficient if it is used during spring time, because during the winter season it's a lack of salt which must be balanced. Don't wait for the autumn.

Even if there's a good food source the Deer will still crave salt/minerals so if there's a deficiency in Your area it may do very well in Your specific Hunting spot!

I don't put minerals out to attract deer. I put them out to supply a little extra nutritional boost. Minerals are the least effective as attractants in the fall-during hunting seasons- anyway. Deer will hit them hard in the spring and summer, but not so much in the fall. Look into products high in calcium and phosphorus and don't worry as much about attracting deer during the season with them. They will visit them every now and then, but nothing like the other seasons.