Skipping upgrades [for drill]

[Nevitar]

Ok, so I have tried searching for this but I cannot find information regarding if it is a bad idea to skip upgrades for the drill.

Say I can afford the Lvl 11 and also the Lv 12 drill.
Is the item boosts compounded or replaced?
So would I earn more total stats from buying both, or just go for 12 directly?
Anyone have any evidence for either or?

[Nevitar]

Using the import/export feature I tested this myself.
An item completely replace the previous in its slot, so it is safe to skip upgrades.

[Finkle]

When at lower levels I skipped many of the upgrades and went to higher ones. as far as I know there was no penalty.