If he is having the advantage of free electricity the option to buy a used antminer s7 and go for Bitcoin is it going to be profitable nowadays ?
How much does this device cost and when do u think he will be able to get his money back and make profit on top of that?
Honestly i'd just go for a bunch of used S5s, they cost less if you're going to use free electricity and you should reach ROI in just a few months and profit after that. You could also go all out with the most obsolete, high-hashrate miners like the S2 but i'm guessing OP has a cap on his electrical usage.