I was looking over this mod to see how you had done things in code, and I have a few suggestions / points of feedback:

• You can set your CustomInputs to use linked_game_control set to "cycle-quality-up" and "cycle-quality-down", instead of hard-coding default key sequences. You probably knew this already, but I was curious why you made them distinct controls.
• You could decouple the mod from the "quality" dependency. It's possible for mods to add qualities without it, but I don't think you would even need to check the feature flag; it should be fully usable without the DLC binary. (The relative UI is useful enough by itself.)
• In your machine.dispose_removed_items function, you say this:

Trash slots are only used by the engine when the recipe is set via circuit connection.

When you change a recipe in Remote View in the standard game, removed items are placed into the crafter's trash inventory. You call this particular function when setting the recipe via the relative UI, and you always insert into the player w/ spilled overflow. When Remote View is used, this overflow appears at the player's camera position (not the character position, nor around the machine).

I understand that it's not really possible to add to the trash inventory and I've experienced this point of frustration in making Compact Recipe Pins (I came up with a workaround but it's not applicable for your case). I have a modding interface request thread about this if you'd like to read it.

The issue with the removed items list in general is that it doesn't include any special data about the items (durability, spoilage, contents of equipment grid).