No they don't, but they are significantly cheaper. Before I added the two plates (I have twins), the Diamond was stern heavy and I couldn't get the bow down to get a decent ride in the chop. I'd tuck the motors all the way into the transom and put the tabs all the way down, and about the only thing I accomplished was to significantly increase my fuel consumption. I believe the extra weight of the 4-strokes on the bracket pull the center of gravity to the rear, making the 12x12 tabs near worthless.
After I added the plates, she was a different boat. The motors are now trimmed closer to neutral (prop shaft approximately parallel to the keel at the transom), and the tabs are much more sensitive. A bit of tab makes a difference. I lost about 1 mph at WOT, but gained a much better ride in the chop, much less fuel consumption, and can stay on plane at about 14 mph.
You could do the same with tabs, but for a lot more money.