Making your own filament
Quality depends on 3 things:


Quality of pellets (purity, fillers, color)
Where/how they are stored before and during the extrusion (humidity, contaminants)
Have a filter in your extruder to get rid of random junk and air bubbles ending up in your filament (250 micron wire mesh filter)



There's no secret formula the filament producing companies have, they just have very efficient and very fast filament producing machines (of course very expensive, too). But when it comes to vanilla ABS or PLA, it's almost the same content.


Personal experience: no. If you get the same pellets, store it in the same place and run your extruder in the same place, it should behave the same.
I don't think there is some filament mixture you won't be able to find anywhere, but you might be able to make it yourself cheaper. Example: mixing strontium aluminate powder for glow in the dark filament (come in many colors, not just green).


I'd recommend this design: http://www.instructables.com/id/Build-your-own-3d-printing-filament-factory-Filame/
It produces filament pretty fast (one full 1kg spoon in 3-4 hours). Just make sure you have enough experience to not electrocute yourself while assembling this as the heaters use mains power.

I personally think the commercial "hobby" extruders are not worth the money. I also own the Filastruder and it's just no different and slower than the above, unless you care about a pretty plywood case for your extruder I see no advantage and since it uses off-the-shelf parts itself why bother buying a kit like that than sourcing the parts yourself?