Used flexi PLA on my Creality K2 Plus
Super slow - no settings over 100mm/s for printing
4hr 24min print time from side spool
First time using any flexible filament with my K2 and it was rough getting it to function.
CFS kind of ate it and even the side spool had some initial issues getting going.
I did not want a rigid print though as I wanted a more rubber or silicone feel for it.
I did make a couple of mold versions, but getting the silicone out clean and full ears was not going well.
So, I printed the frame instead of casting from the mold.