I hope your new sender is adjustable, so it can accurately represent the level based on the shape of the tank- if that is important to you.
The sender that ships with the car is designed to do just that- it understands the tank profile, and has a curve that offers resistance at the correct level, so that, for example, half resistance is really half full.
Using a normal lever/float type of sender, or even a standard capacitance sender will result in inaccurate readings, not just for the Koso gauge, but for any standard gauge. For the tank profile we have, they tend to overstate the fuel level, mostly at the top. It should be more accurate as the level gets low, as the tank becomes square at that point.
The point is that just because you have a gauge and a sender that have a matching resistance profile, you don't necessarily have an accurate level reading- you need to have a sender that can accurately represent the level in your tank- which senders that are not calibrated to the tank profile do not.
Luckily, because the tank approaches a square or rectangle at the bottom of the readout, the most important part of the readout should be fairly accurate, no matter what system you have, assuming the rest of the setup (e.g., lever/float travel, height above the bottom, etc) is correct.