Just an opinion but...
The square bottom of the Easywood to ole ensures that the tool remains in the correct position. A rounded tool handle in the case of a square cutting tool is somewhat dangerous as the wrong angle could cause a catch. I have not used these but have used the Easywood tools. These tools are aggressive and it could potentially become dangerous. In addition, the square bottom ensures if you cut too deep, the tool will not rotate out of your hand.
I assume that Easywood has this square shape patented or everyone else would be making the same tool at a more reasonable price.