If you look closely, you will notice that the feed dogs on the Featherweight (221) are very narrow and shaped differently from many other Singers. It is helpful to have a good "line-up" between the walking foot and the feed dogs. The Featherweight shop as mentioned before sells walking feet with the correct line-up.
It is hit or miss with generic short shank walking feet, and some are more successful to use than others.
Concerning the plastic shank, the only problem I have had with those walking feet is that they eventually break. It is not easy to find a metal one. Part of the connection problem is that the standard screw for FW feet does not have a slot for a screwdriver and is tightened by hand. You can use a screw from other FW attachments that have a slot and then be able to get things tighter.