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.
With all due respect @bettercrypto, there are several things that make me doubt about your answer. This topic was created in 2015, I don't think there's any point in answering OP's question anymore, it hasn't even been connected since "03 December 2015, 06:26:46"
What's more, even the pure content of your reply doesn't seem very appropriate to me. Comparing a USB miner with a few tens of Gh/s of hashrate like the U3 and an S19 makes no sense. At the time he wrote this topic the S19 didn't even exist.
Even today, it would never occur to anyone to compare the performance of an S19 with Gekkoscience's products, for example. It's a nonsense in my opinion