Yes, you have bump steer, the question is, how much? Because of the dynamics involved in front end geometries, pivot points of upper and lower control arms and tie rods, and the amount of camber and caster, the tie rods do not swing in the same arc as the control arms. I don't believe ours have as much as the earlier Mustangs, just like we don't need the "Shelby drop", Ford did a better job on the front end geometry.
Whether or not you will benefit from the aftermarket "solution" will depend on how well they did their analysis of the geometries involved, whether or not they actually tested the results, and whether or not it's a one size fits all years solution.
Here's a decent article that explains it well and shows how to actually test the amount of bump steer
http://www.mustangandfords.com/how-to/chassis-suspension/mufp-0611-bumpsteer-explained
If you decide to follow through with checking yours, it will make a great tutorial/article for the forum.
Edit: A front suspension that is in good condition, good springs, sway bars, bushings and ball joints, will reduce bump steer and help mitigate it when it does occur during hard turns and going over humps and dips.