I repeatedly left clicked an ore and it gave me already extracted minerals, making the extractor useless and meaning I only need one ore to get unlimited materials.
Manually getting ore from veins is an intended mechanic. Veins give infinite ore with the extractor or manually mining.
Where you getting materials faster than just holding left click?
Browsing the blocks on the screen on the left was hard because the details for the block are way over on the right. Might be ok on a laptop screen but it was too far away on my 27" monitor
Have you tried playing with an increased UI zoom level? (in the options menu)
An undo function to a sandbox game would be VERY difficult to implement, and anyways I like the need for scaffolding to build
