Update: Uploaded V2 of the simple filament guide, this should make it easier to pull the guide out when necessary. -- I have tried a few versions of Brook Drumm's filament guide, from the laser cut one shipped with my kit to a customized plastic guide found here on thingiverse. Even after making my own modifications to make the fit better, none was quite secure enough to keep the filament straight or keep the filament from buckling. I decided that a block to sit INSIDE the assembly would fix the issue - Absolutely secure and impossible for the filament to get off track. I've run a few prints off since making this and have not had any binding issues.