Make sure your read about zombie's on U3. Unless you have a plan in advance to deal with it your going to hate the U3. It's just a truth zombie's without automation to fix kills them being much fun. And you will not ROI on a U3 just math does not add, you can run it yourself:
https://bitcoinwisdom.com/bitcoin/calculator Make sure to have difficulty changes with it.
Phils idea of S1 is not a bad idea if you get a good deal. But again run ROI math. Even with free electricity do a ROI to make sure you will get what you paid for miner back with difficulty changes. U3 I can promise you will not get it back.
walk me through to use the calculator please, i new at this