I have the Bissel Pro. Love it. Even tho I only have area rugs, it still gets used every other month. One way we learned to keep the carpet cleaner was to make sure shoes came off at the door. That means EVERYONE!! Doesn't matter if it's a handyman, deliveryman or guests. If they don't want to walk barefoot or in their socks, I have slippers they can use. They can take them home afterwards if they'd like too! :)
That seemed to cut down alot on the dirt being trafficked in.