garcia.logan hit it on the head with "keeps everything under the brine so much easier." I actually went with the glass weight because I'm too cheap to buy new stuff and my friend gave me their old one. First batch went fine until I dropped it on my foot while cleaning up. Broke a toe and had to eat sauerkraut on the couch for a week. Spring might have been safer for my bones at least.
Totally feel you on the glass weight thing. I switched last year and it was a game changer. My veggies used to always float up with the spring, no matter how tight I cranked it. Now everything just stays put, and cleaning is way easier too. I don't think I'm ever going back to the old way.