Charging

• The Roomba 4210 can return to its battery-charging docking station with the push of a button, but the 510 model cannot. Both units have rechargeable batteries.
  
  

Cleaning

• The Roomba 510 can sense particularly dirty areas and spend extra time tidying those spots. The 4210 model does not have this feature.
  
  

Tangling

• When the 4210 bumps into cords or string, it sucks up the item, disabling the device. The 510 has anti-tangling technology. When it runs into a cord and begins to suck it in, the 510 reverses direction and spits out the hazard.