One reason for the Plastic one is that you can see when there about to run out if there a top loading
bobbin, where as the metal ones you can't really see if they are almost empty.

Metal tends to wear away the drop in bobbin cases so I would recommend the plastic bobbins for those. If you have a removable metal casing that you put the bobbin in, the metal bobbins work good and there is not a "wear" factor.

My old sewing machine had a vertical bobbin case and I used metal bobbins with it. I do actually prefer the metal bobbins, but my new sewing machine requires the plastic bobbins, so I've made the sacrifice.

I have a Janome 7700 and haven't noticed a difference whether I use the metal or official Janome bobbins. The metal are easier to fill as they have more holes to get the initial thread in before I wind it. :) The plastic only have two--the metal has dozens. Easier on the eyes.

My 23 year old Viking uses plastic bobbins and my 11 year old Bernina uses metal, both have metal bobbin cases. I've never even considered changing what they came with; I won't even buy generic bobbins for them. Bobbins are too important to mess around with imo.

my kenmore came with plastic and my juki came with metal. but i use cardboard prewounds in both of them and have no issues with them.

I use both in my old Singer 401A, but metal only in the others, only because that's what I have.

Both my Pfaff and Viking came with plastic bobbins. This was a first for me. I have noticed a chip in one and tossed it. I guess it might be something you would have to replace from time to time. I do love the alert that thread is running short so a small price to pay.

I use both so I am not much help. Yes they are both used on the same machine and I have done this for many yrs. Bobbins come in different shapes so keep that in mind.

Someone had posted you can use plastic instead of metal but not metal for plastic. Newer machine have plastic parts & metal wears them