I modified a standard prusa nozzle to test the filament joining nozzle. I found a steel tube and inserted a PFTE tube that has a 1.75mm ID inside it.
I inserted one filament piece halfway through the joiner component. I then heated the joiner up to 235deg C and pushed the second filament piece through the joiner. The two pieces were successfully fused together.
The key concern is that the plastic is crystalized and solidified but the high heat. But it still seems to be relatively flexible.
[Figure 1: Filament pieces before being connected]
[Figure 2: Closeup of filament pieces after being connected]
[Figure 3: Filament pieces after being connected]