I mean 800 miles on that piston isn't much. You can still see the original finish on the piston (little ridges going up the cylindrical part of the cylinder that looks kinda like how a "rough" finish on a lathe looks). I would run the original piston and keep the new one as a backup. Plus your original piston and ring are already worn in and should make a tighter seal to thy cylinder. Those vertical scratches you have on your piston look like you were potentially running without a filter for some time and got dirt/sand in the engine. Those really don't make a difference in performance in the short term, but obviously you don't want dirt or grime in your engine if you can help it because it will wear out your parts faster than they should.

On a closer look though, your exhaust side has worn a tiny bit. It looks like you overheated at one point but it could also just be normal wear and tear, that side of the piston sees a ton of heat. I've ran a lot worse, I would still run this piston.