I see everyone here using ABS on an open spool.
My PLA on the M3D mostly requires feeding via an Airtight spool holder bottom lined with desiccant. I am using a 'Filament Safe' from Perceptioneng.com.
Any reasons why I should stick to the open air side stick holder rather than feed via a teflon tube and keep the ABS in the same setup (no moisture/dust exposure)?
No problem using it. Lots of people have alternate versions of the same concept with no problems
One thing on the dust though, a lot of the Zortrax filaments no longer come in vacuum packed bags and are now stored directly in the cardboard box with some plastic wrap around the filament. The filament spools are usually covered in box dust and the plastic wrap doesn't cut it to prevent it :P
Suggest printing "Threaded Filament Dust Filter - Universal" (or similar) at thingiverse