An update: i just asked them, by contact form, about payment security and they immediately answered they use:
https://bitpay.comI don't know it but it seems like a paypal/escrow, this could be a sign of seriousness.
In any case searching on aliexpress, I found it's possible to find cheaper usb miner (not the erupter one but the ones >1.6 gh/S), considering that on bitcoin-world they ask 0.1 bitcoin, at the quotation of today (620/bitcoin),.