If you ask me, it is not good to use this Bitmain AntMiner U3 Bitcoin Miner Version 2, because its hash rate is low, and then the lifespan used is also short, if I am not mistaken, you can only use it for one year, which after 1 year you have to buy a new one again.

So I think the best one to use or to buy is the Bitmain Antminer S19 Pro, it is better because it has a higher hashrate than the U3, secondly its costing is lower than the U3 when it comes to electricity. In short, it is more profitable to run and to use compared to the U3 version 2 you are talking about.