I tend to stop using free plug-ins after I've eventually added one that I paid for that has more robust features.
I guess it's like working out at the gym. I could exercise for free on the street. Or I could pay a little and have specialized equipment in a specialized environment to tone my physique just right. As long as I've paid for the membership I might as well use the equipment.
There are obviously free ones, or plug-ins included with Sonar, that are great and totally worth using regularly. But if I've bought a cool plug-in I'll probably try to get my money's worth out of it, rather than reaching for a free one also on the menu list with less capabilities.