Great battery really boosted my watch's battery life.
I worry about OEM batteries for old products because the batteries are often old too. But this battery really put some life back into my Gear S2. I think the battery was intended for a slightly different version, but with a few clever adjustments to the folds in the ribbon cable, it fit fine and has performed better than I expected.
The battery is good quality. It seems to be an exact replacement for the original. However, this battery comes with some tools and the tri-point screwdriver that it came with was too small to remove the screws on the back of my Samsung Gear Sport watch without stripping them. I had to buy a 2.0mm tri-point online to complete the replacement.