The problem with block eruptors is that the cheap ones aren't so cheap anymore. I bought 8x 333 MH for between $24 and $33. There was a time they were cheaper. It's taken me a couple weeks to pay off even one of them.
Now they are upwards of $70 or more. Haven't looked in a couple days. I'm contemplating resaling them and just buying btc's. lol
The problem with block eruptors is that they aren't miners.
At the price per GH , you can consider them some novelty or a cool keychain that you cam play with it when you're bored.
Even at 20$ , that would make it 60$ per GH , I won't even dare to compare it to a Knc miner.