This mod is perfect!
I never liked the vanilla toolbar, and always just left it empty. It was too much hassle to manage.
This mod fixes all my issues by making it automatic! I never want to go back to the old system.

I have a small suggestion if you don't mind:
A per-player setting to lock the gui position. Sometimes I knock the gui out of place when trying to click a machine.

Yeah same here. Also never liked the vanilla toolbar and left it empty. But with your mod providing a kind of automatically filled toolbar it really is fun to use that. I did misunderstand the mod description in the way that the placeables GUI shows ALL POTENTIAL placeables that you have already researched. Now that I see that it only shows the placables in your inventory (and even aggregates them if you have multiple stacks) I am positively surprised that the mod is even cooler than I expected!! A must have mod!! Thank you for developing this :-) PS: I recommend that you update the mod description by adding "all items THAT ARE CURRENTLY IN YOUR INVENTORY you can use for building"

Also the mod's title could be more helpful by saying "Placeables: Compact view of all placeable items in your inventory"