The plastic coating just makes them look nice. Because it is a thick plastic coating, they retain their shape and slide easily onto bars, no folding down of edges or crimping required, so easy for uniform restoration projects. However, due to the thickness, holes for devices have to be pierced/bunched, devices don't just push on like with other ribbons.
That said, they are overly glossy and from the portraits in my collection, I don't think they were as popular with service members then as they are with collectors now, which is probably why it seems far more unused stock is in circulation than constructed bars. Back then, troops wanted the cheapest ribbons, and they just pushed devices on. These were probably too much work for the average draftee who rarely wore them anyway. They'd probably be universally endorsed in today's military, where a crooked star will get you shredded by a 1stSgt
I only use them in restorations if I have evidence the veteran did.