The three are the same ink at different capacities — standard, high and extra-high. The important point is that 405XXL black does not fit every printer in the 405 family. Machines such as the WF-4820DWF take 405 and 405XL only. Buying XXL for a printer that doesn't accept it is an expensive mistake, so check your model before ordering the largest size.

Yes, and volume is where it pays off most. The WorkForce Pro range is built for steady output, so the more you print the bigger the gap between compatible and genuine Epson prices. Text stays crisp for letters, invoices and reports, which is most of what these machines do.

Yes. There is no problem running a standard cartridge in one slot and an XL in another. It's useful if you get through black faster than colour, which most offices do.

Keep them sealed in their packaging, upright, somewhere cool and out of direct sunlight. Unopened cartridges keep well for a long time; once the foil is opened the ink can begin to dry, so only unwrap one when you're ready to fit it.