I like glass negative carriers. But many hate them because they require more cleaning. The guarantied film flatness lets you keep the lens open wider and still be assured of good focus. Without glass you sometimes get a wavy negative (especially for 35mm and 120 film) that isn't fully sharp without stopping the lens down more. Glass also means you don't need to worry about buckling from the heat.

I don't have any experience with either lens. I have 100mm Componon S and it's a good lens. I don't know if it's better than what you have; but the Componon is an older lens compared to the newer Componon S. I suspect the Vivitar is bargain lens based on the slower speed for a 50. I have used a few different 50s and like the Nikon 50mm f/2.8 the best. They are also easily found for not much money. But try the Vivitar out first - it may be good.