Along with the spade and fork, the hoe is considered a basic, essential hand gardening tool.
The conventional garden hoe has a flat rectangular blade set at a sharp angle to the ground and is designed to move more soil than weeding hoes. It is typically used in a chopping motion. "The basic (conventional) hoe has a wood handle with a solid, flat head that's useful for cultivating soil before planting, but it's not the best weeder." (leading Consumer Magazine test of Hoes and Cultivators)*
The conventional hoe has many disadvantages for weeding and cultivating when compared to a circlehoe. It has so many resistance points that it makes the job of weeding very stressful on your body.
Flat bladed hoes tend to drag soil away risking exposure & damage to a plant's root zone. It requires extra effort to re-adjust & groom the soil. Compared to the curved circlehoe blade, a standard hoe's flat blade has more resistance when pulled through the soil.
The unique shape of the blade does not drag the soil along reducing much of the time required to re-adjust & groom a cultivated area. The circlehoe works very well in difficult soils like Clay & Adobe because the sharp, curved blade has less resistance when it enters & is drawn through the soil.
Hoes with sharp and/or pointed edges can damage the stems and roots of plants. Because the blade is hidden under the soil, it is difficult to judge where the blade is actually cutting. The result is often undercutting the root zone of your plant.
The sides of the circlehoe blade above the sharpened area are dull so that any contact with your plant will not damage it. The sides also act as a reference for the position & depth of the blade. You can see by the illustration that the curved blade is not in a position to undercut the roots as it passes by the plant.