One of the most important features of my 440QE is the needle up/down with the button on the head of the machine. When I need to sew exactly into a corner, I can do the last few stitches with my thumb, and never over-shoot my stopping point.
A feature that I need to learn is the presser foot up/down with the knee lever. I know several who do that and love it. It takes persistence and patience, and I should take the time to do that. Trouble is, my old machine is a 1956 Singer built into a desk with the foot pedal mounted on the side of the inside of the cabinet. I love that feature. My pedal is always there. And I use that machine a lot, too, so it is very easy to get confused between the two operations that happen with the same action.
As for the needle threader, I love mine. But I find that the more I use starties/stoppies, the less I have to thread the needle.! ! ! LOL