Yes one is a circle and one is a semi circle, but they work fine together as long as they both have the same upgrades. By design the Planter needs to be in the center and the Harvester on the outer middle edge.
The planter plants a 3x3 grid with itself at the center. The harvester harvests a 3x3 grid with itselfs at the middle outer edge.
So as long as yoru planter is always in the center of your grid and the harvester at the outer edge in the middle and they both have the same upgrades you only need 1 of each.
IE : X = trees, P= Planter, H=Harvester
default 3x3
xxx
xPxH
xxx
Iron upgrade in both (adds 2? Not sure if that is the correct size not at my home PC)
xxxxx
xxxxx
xxPxxH
xxxxx
xxxxx
and so on.