I prefer the polymer jar when screwed into my MK3 and used as a catch cup. It's lighter and screws in tighter so I don't feel like it could unscrew by itself while i'm grinding. Only downside is when used as bean storage jar - I can faintly smell the coffee inside the jar even when closed tightly, suggesting it's not airtight without the white paper seal that the glass jars had. When storing ground coffee when going out, I get a strong whiff of coffee even from my bag under my desk.

I can't speak for the included glass jar with the Mk 4 Comandante, but this jar is much better than the Mk 3 Comandante's glass jar.
There is no inside lip below the threads which grounds can get caught on and the polymer jar also holds less static so coffee grounds, especially fine ones, are much less likely to stick.

Love these for pre dosed coffee on the go. I use these to grind at home and have pre dosed coffee to take to the office for my pour overs. I love that they are not glass, and the variety of colours.

These jars are much better than the glass ones. You cannot possibly break them plus the colors are very fun. Thanks to Eight Ounce once again for the super fast shipping.

These jars are so beautiful and versatile. I find that this is also perfect for rdt.
I am definitely recommending this product to everyone. Color on this Jar is absolutely stunning to see.