I printed lawzzys filament guide doohickey on the first few days and its been performing like a champ ever since, if you keep it fairly vertical it acts as a 'jerk remover' as well as a filament non return valve as such as well.

I grew up in a Manufacturing environment working with wire forming equipment.  One of the things we always had to make sure of is that the infeed was always smooth and jerk-free.  I designed and printed this flexible arm to absorb sudden tugging when the extruder is heading from back to front rapidly.  Not sure if it makes any difference in print quality, but I do like having it on there!