If the machines are making that much bitcoins, why are they selling them so fast? I don't think they made their ROI in just a few days.
They aren't making anything by mining - it's advertising speak.
My 2 ASICMiner Blades are making 1BTC every 40 days, rough estimate, at 511Mil difficulty. That's at ~12GH each. That means the 10x Block Erupters are making 1BTC every 160 days. Each single one takes 1600 days, which is 4.38 years, assuming difficulty stays at 511M. Which it won't.
Totally pointless.
The ONLY way to make money from Block Erupters is by selling them on eBay or Amazon to suckers. Period.