The previous sensor didn’t work well with some specific filaments. The new sensor is using the optical sensor which is triggered by a simple mechanical lever. This sensor doesn’t care about the optical properties of the filament (it can be completely invisible) and cannot die because of mechanical wear.
Thanks to completely reworked extruder you don’t have to take apart the whole extruder if you want to change the nozzle or PTFE tube. As a bonus, the nozzle and the extruder motor is much closer to the X axis, this means less resonance and better prints too. Better Y axis belt tensioning is just the icing on the cake.
Thanks to the better design of the whole extruder, air flow is increased and as a result, cooling capabilities are improved. We have also focused on cooling of the the printed object and MK2.5S/MK3S is better for printing from flexible materials.