I've built one and it came out very nicely. I'm very impressed with the scad file...it is very well organized and commented. The holder can be customized to fit your spools exactly. It took nearly 7 hours to print on my prusa i3, just for the base with the retainers, but that's just how it goes.
I've discovered that a US 5/16" bolt is very nearly the same size as an 8mm bolt, and much more economical if you live in the US (0.3149" dia for 8mm; 0.3125" dia for 5/16). Of course it won't work if you're threading it into 8mm hardware, but just acting as an axle for the bearings, it should be fine here.