Solve a harder proof if you don't want to waste ETH.
The miner lets you set a difficulty of once every 10 weeks if you want to
aka 0.1 proofs per week.

It uses a lot of CPU power and at best you'll make what? $2-$4 a day?

Still, just the fact that Koin can be mined makes the current price per token very low (3 cents) while at the same time being highly resistant to dropping lower than that due to mining costs. Pretty good deal to just buy Koin straight up for 3 cents per and watch the price skyrocket in 6-12 months.