I have used the K8203 extruder kit and it is a lot better than the stock extruder. The direct drive works very well, and the kit is easy to build.
The hot end that comes with the kit is also very good, and gives better print quality than the stock setup, due to the smaller nozzle. But it can be susceptible to jamming.
I have replaced the K8203 hot end with a E3D V6 hot end, still using the K8203 drive mechanism. This is probably the best performing setup due to the improved heat management in the hot end. I had to slightly enlarge the hole in the mounting bracket, and I designed a small adapter to enable mounting the E3D onto the K8203:
Keep in mind that this upgrade means your 3mm filament will no longer fit in your printer. You’ll need to use 1.75mm instead.