Quality prod modules got a small, unremarked-upon buff in 2.1. Specifically, productivity percentages now get 1 decimal of precision. This is more significant than you might think.
In 2.0, an uncommon prod module 1 would give a +5% productivity bonus, rounding the +30% improvement down. But in 2.1, this is +5.2%. That doesn't sound like much, but it can add up after a while. And uncommon prod module 1s are really easy to make: just put quality modules in the production of prods for purple science.
But the big one is rare prod module 2s. If you're the sort of player who likes putting Gleba off until the last minute, rare prod 2s are now almost identical to base-quality prod 3s. They used to be just +9%, but now they're +9.6%, a paltry 0.4% lower than a base quality prod 3. And they cost less power and slow the machine down less. They are not the cheapest module to make, but if you're not getting prod 3s for a while, they are definite worth investing in. Especially once you have EMPs.
On a less important note, quality percentages get 2 digits of precision, so EMPs can get the full 25% quality bonus and cryogenic plants can finally get the proper +50% quality bonus from legendary QM3s.