Pressure side Cleaners either work with a booster pump or off one of your return fittings.  The Booster pump cleaners are more expensive and Naturally require a booster pump be plumbed into your system requiring more installation.  An pressure side cleaner that works on your existing return lines do not require a booster pump.  Both of these style of cleaner pick up the debris in there own debis bag so they do not clog your filter.   They also will not suck large debris into your pools lines as suction cleaners will.