The pretreated stuff does work. My oldest pretreated clothing are T shirts from Insect Shield. I estimate they have been through about 50 washes and are still working. When I used to spray my clothing with Permethrin, I'd get about 4 or 5 washes out of it before it faded and became ineffective.
I liked it enough that I now have several pairs of pretreated pants, short and long sleeved shirts, and socks (Farm to Feet Boulder "No Fly zone" socks are great!). It's been nice not have to keep track of when the last time I sprayed my clothing was.