I used regular/cheapest filament they have for almost 2 years now. 1.75 mm. Neutral, gold, yellow, red, blue, green, silver, pink. There are some behavioral differences depending on color, but this is normal. Pretty consistent diameter, slightly lower: 1.70-1.72 mm. Simple and compact spool of 1 kg (I bought also some 2 kg spools). Works well at 250/110 Celsius (hotend/bed). Don't know where is produced, but I can guess is China.
What else?