In My Not So Humble Opinion, the 401 and 500 are the best multi-stitch mechanical machines Singer or for that matter anyone else ever made. There is no plastic in them to fail. They are all steel inside.
We have one 401a and two 500a's and if I were forced (it would take an act of God) to divest myself of all but one multi-stitch sewing machine, it would be one of those two I'd keep.
Anyone that has the chance to get one of these machines for a reasonable or cheep price should not hesitate. Grab it fast and run for home with it. Well, pay for it first of course. Nothing a 401 could need is so expensive that it's out of reason. All the accessories and cams are still available, manuals are free for the downloading at Singer.
There are cases for them, cabinets and tables. Very flexible set ups.
Joe