I use a snap although I didn't used to for many years. The thing about tying directly is that occasionally the knot will get pushed to either side which will cause the lure to run crooked. You can just push it back to straight but that get's old after a while. I also believe that the knot gets weak over time when tied directly to the eye because the eye on the slammer is pretty wide and it makes the knot chafe back and forth. In addition the snap allows the plug to kick back and forth a little better I feel.