The SSD8825 is unique compared to other stepper drivers becuase the components are mounted on the underside of the PCB with the top exposed for easy heat sink mounting. The driver chip has a heat pad at the bottom of the case that allows heat to be drawn away from it. By having the parts at the bottom you can now attach a heatsink that is thermally connected to the heat pad thereby cooling the chip better compared to attaching the heat sink on top of the IC.
The SD88825 comes pre-soldered with special 0.1” pitch headers that are taller than what is commonly available. This gives more space at the bottom to protect the parts from shorting into something and allows air to flow more freely on the underside of the board.
The SD8825 drivers are known for their robustness and very good thermal management due to its unique design layout. These are better performers compared to other DRV8825 drivers out there.