I have a set of the plastic ones......made from recycled milk jugs I think..... They are STRONG !! But the problem I have with mine is getting up on em. They slide across the shop floor...... Yes, they have a rubber foot imbedded in the front bottom, but they still tend to slide.
So I put mine outside just on the entrance to the concrete so they have something t o butt up against, that way they don't slide around.
I like em, they come in handy.
Buy em, but use common sense with em like any other jack or stand, block the rear wheels. Work Safe !! "BH"