I did the "missing link" on my 03 Ultra and 05 Road King......the difference is noticable and they were MUCH more stable. At 2 up or high weight its more noticable, in a word....yes it makes a difference. Do your homework though, not all links are created equal. I chose the missing link because it replaced the swingarm pivot bracket, rather than adding a bracket to a frame stiffener. I believe that it is stronger there....JMO mind you. I also liked that the pivot point on that model was in line with pivot point of the swingarm. I havent looked at any of them lately, but True-Track is the ONLY one who makes one for my ol'girl, I havent bought one yet, but Ester is much more stable with the late model swingarm.
Hope this helps.
1989 Tour Glide "Ester"