I think it depends on how big your plot is. When we planted our 2 acre clover plot, we didn't bother putting a plot saver in because it was just too large to worry about the deer mowing it off before it could get started.
When we planted a small (1/4 acre) plot of full draw last year, we had put a plot saver around it along with a trail camera. The first week after it started coming up we had 3 pictures of deer inside the plot saver, but no real damage done to the plants. We figured that the plot saver was worthless, so we took it off and in less than a week the entire plot was gone, I couldn't believe it, every single leaf of every plant was completely chewed off.
Long story short, plot savers won't keep every deer out of your plot all the time, but they will help protect your young plot from being completely destroyed before it can get a start.