That was super fun! I activate 3x speed from the start and the rush feels really good. the pacing also feels nice and getting the upgrade feels really smooth, easy, but also challenging for the later one without requiring too much grinding.
However, I do have one complain, and it's the fact that you change the position on the keep digging button and the reset run button between the first time you beat the game and the subsequent one. I almost reset my run even though I wanted to continue digging to upgrade the rest of the upgrade (I was glad you have a confirm button to make sure I didn't do it, but that still could be accidentally clicked on if I didn't pay enough attention and just thought "oops, didn't hit the button correctly")
other than that, fun game! Would love to see how you continue the game further and what upgrades you'll add.