I saw it through to the end. I paid the 9,999,999 and then did two upgrades.
I'm not a fan of active clickers (where I have to click myself), so I stopped upgrading the manual tool. I got it up to 1024 and then called it quits; just boosting the auto-clicks was enough.
I'm not sure what to say—it's a mini-game, and it works. Admittedly, it got a bit boring; I went AFK on YouTube while the wood gathered itself. Everyone loves seeing those big numbers-per-second go up :D