Hello! I decided that there should be dedicated thread for quality so i can post my feedback there.

Right now i found that concrete blocks are made in one step only from liquid concrete so they are very hard to bring to legendary qualty.
I suggest adding new lategame recipe for them to take a solid ingredient so they can build on it's quality:

10 liquid concrete and 1 concrete scrap = 1 concrete block

This recipe will be more wastefull than original one, but with it it will be possible to integrate concrete scrap into blue science production chain.
Right now i have to totaly waste tons of concrete trying to get a trickle of legendary concrete.

Also looking at rubber: simple recipe without seeds and no module slots in forestries means that there is no quality wood, and making rubber is only 1 step with 2 module slots in crusher. Situation would be dire unless there was a recipe for synthetic rubber that takes nickel pellet as a solid ingredient.
So the only meaningfull way to get legendary rubber is by using legendary nickel pellets. While this may be unintentional yet is rather thematic and i like that.

Quality modules can be placed into canning/barreling machine in emptying mode but not in filling mode, i thing that using quality modules in these machines should be prohibited.

May be posting more about quality in future.

Quality is mostly something that I have added because it is a requirement for Space Age, in the event that third-party modders want to try making a Space Age add-on for IR3. I have no expectation that Quality during the usual IR3 progression will be balanced or in any way practical to use.

That being said, I will make a concession for this one recipe. I don't like that "Holmium solution" exists in Space Age to erase quality from Holmium ore, and since I know that Deadlock didn't create Liquid concrete with the same intent, I'll add in this escape hatch to get around it.

10 liquid concrete and 1 concrete scrap = 1 concrete block

This recipe is called "Concrete block using Concrete scrap", and it's unlocked with the "Concrete 2" technology only when the Quality mod is active.

Quality modules can be placed into canning/barreling machine in emptying mode but not in filling mode, i thing that using quality modules in these machines should be prohibited.

I've fixed this as well on the Codeberg build.

I don't believe I will be changing anything about Rubber production.

I would like to wait until Factorio 2.1 if I were to ever do a balancing pass for quality recipes, because modders will have much more control over enabling/disabling quality inside a recipe.

Until then, you may like to investigate the Recipe Tweaker mod, which will let you make your own personal changes to recipes.

Thank you!