After struggling to print TPE filament on my Kossel Mini delta printer (nowden extruder), I decided to go back to basics and design a new extruder that incorporates the features needed to print this extremely flexible filament.
The main point of the design is to keep the "exit hole" as close as possible to the feed gear to remove the possibility of it kinking and jamming. The other design point was to have the entry and exit holes perfectly aligned with the edge of the drive gear, to keep physical resistance to an absolute minimum. Being a bowden extruder, this reduced friction also dramatically improves it's performance with very rigid filaments such as PLA.
I've also learned through trial and error, to not only keep the speed very low (I found that 10mm/sec was 100% trouble free), but to keep the pressure on the idler bearing as light as possible so as not to damage or destort the filament in the slightest as it is being pulled through.