That's why many people prefer to claim the faucet only instead of using the mining feature. It will be just a really bad idea to use the mining, but I wonder how many people using it because I see some people support this feature as a great feature to earn free satoshi without doing anything.
I personally use it a fair amount, and run it on my work computers with 4 threads at 80%, getting 40-50 H/s. It's pretty decent, I've gotten about 20,000 satoshi total so far from using it!