Tim here, from Filastruder.
With the melt filter, dirt and other contaminants are not a concern.
The nozzles I provide are closer to 2.9mm output, depending on extrusion temperature. If you need a slightly smaller diameter, you can up the temperature. If you are really worried about hitting 2.8mm, you could buy a 1.75mm nozzle and drill it out in increments, or email me through the FIlastruder website and I'll custom drill a nozzle for you.
Happy printing!