I don't have a metric ton of mags, but all of them have green followers and function 100%. I recently priced some new mags from one vendor: 10 mags w/ green= $89.95. Those same mags with Gen2 Magpul followers= $111.85
From another vendor, again with Magpuls= $109
The argument is made that green or black followers can tilt and cause jams, so go with the best. I agree.....if you are running your AR hard, in less-than-optimum conditions, and relying on it to save lives.
Just yesterday, I spent a few hours shooting ARs with another board member, and neither of us experienced a failure of any kind with the green followers. Yea, we weren't shooting fast, dumping rounds downrange and working in dusty conditions. If you are, get the best stuff on the market to limit your chances of dancing with Mr. Murphy.
If you're looking at a bulk mag purchase in the near future, you might as well get the Gen2 followers already installed for the simple reason that I can't hurt and doesn't cost that much more. If you are experiencing problems with a particular magazine, changing the spring and follower with better might just fix the issue. Otherwise, run with the green and don't feel left out.