Pens are definitely superior. I used to do 1mm, but I switched to 1.5mm in the last two months. I tried 2.5mm, but it was too painful. Maybe I'll try it again with a numbing cream.
12 pin or 36pin cartridge, i was using 36 pin, dunno if that's why it was pulling out so many hairs. I was needling at 2.5mm and the pain wasn't all that bad, on my crown though, maybe temples and stuff are more painful.