Quality in Efficiency Modules interferes with already existing designs where efficiency modules are employed to reduce power consumption. Addition of quality to regular efficiency modules would result in efficiency-utilizing machines suddenly producing quality products, which would clog entire bases, making this mod impossible to integrate with an already existing run.
With this mod, you effectively get quality modules you can put inside beacons, without a speed penalty, which can be stacked with productivity, and on top of all that, used to make uber-quality setups with beacon spam.
The mod's idea is good, I personally like it, but its implications are far-reaching, just like "vanilla" quality (to remind you, 25% productivity bonus in a single module is insanity).
As for my idea: Efficiency modules should not be touched. This mod should add dedicated efficiency-quality modules which provide a much less quality and efficiency benefit, however they should retain the ability to be used within beacons. This way, they can't be used as quality modules without the speed penalty, but work as a counter to speed modules, as per the mod's original intent.