well, for one thing there are no circuit boards to go blooie
there are no plastic parts, gears, etc to crinkle, fail, break, dissolve
they are cool as all get out
get a treadle or handcrank and you can sew anywhere, anytime, with no electricity
and as she said, perfectly straight stitches - watch a zigzag machine stitch a 'straight' line sometime - you will see teeny tiny deviations to the sides..