One thing to keep in mind is that you'll get scratches on your wheels with the aero covers on. Dirt gets trapped under them and the micro vortices of air while driving cause the dirt to scratch the wheels. Happens on the Dream 21s too. If it doesn't bother you, no big deal. If it will bother you, then pick one - always on or always off. I also think the clips themselves might scratch a bit with putting them on and removing them.
Because of this, I decided to just leave mine on all the time, in part too because I bought them used and they already had the scratches.