There's no danger of doing any damage to your computer. Also, you can set the % low so that you don't stress out the CPU and you can continue to use the PC at the same time. As to whether it's worth it financially, we don't really know yet as Wetsuit hasn't finalised the mining reward. This will happen after testing is complete and it has been rolled out to the whole userbase. Then we can work out if the rewards cover the cost of electricity.

I really don't think it is mining BTC directly, I assume it's mining XMR and that's being traded for BTC.