My wife's first ZZ machine was a Singer 538. It's on it's third set of plastic gears and has so much wear on another gear we're going to have to replace it. She keeps avoiding buying the parts.
We've bought two Singer 413s and within a couple hours of sewing the vertical shaft top gear has shattered.
I do not, and can not trust a plastic geared machine. The Singer 4622a we have is all plastic and works well ... so far. But it's rarely used.
The Bernina 930 my wife inherited is doing well and she uses or did the heck out of it. When the plastic bits die, I'm not sure what she'll do. But it will be her it dies on cos I won't use it.
I prefer my older machines with removable or built in cams and all metal gears. I have no problems with those old ladies. They are like the EverReady Bunnie ..... they just keep on going ... going ... going ... going.
I just cannot see paying thousands of dollars for a computerized piece of plastic. To my way of thinking that's insane. No insults meant to those that have them, but that's the way I feel.
Joe