Not much in the line of changes. Same inks as the 300 series. The 6400 can now accept 300mL tanks for a larger option. Minor improvements to screening, so slightly better and faster prints than the last generation.
If you're several generations behind it might be worth an upgrade, but there's nothing amazing separating the 300 and 400 series printers.
If you're buying for the first time, they'd be a fine option.
