The curb style is generally set at ground level for lawn mowing. It is very popular in commercial lawn settings because it handles larger mower wheels and has a more massive look. It can be installed as regular gray concrete or it can be stamped and textured. Because it is set at ground level it is not as easily seen from the street and therefore leaves a groomed look without seeing as much concrete edging.
This style can be used like the regular curb style or it can be used as a retainer. The 6X6 is sometimes the spec that is used by commercial architects and it is simply placed deeper in the ground. Other applications may include retention of gravel, gardening materials or other driveway or walkway situations.