So sorry for not seeing this comment @adoris till now, your comment got missed somehow and I apologize for that. Yea I wouldn't invest in any BTC miner that is usb based, least the older stuff, well actually I don't think there is any new ones to this day that actually will earn you anything. Reason is the difficulty is insane now to mine BTC directly even with a GPU and also on some other coins. Its at a stage where its just for those with serious hash power on BTC to really make it worth mining. I would suggest at minimum now a days to stick with GPU mining or Asic mining if the money is available to do so. Sad though, at one time USB mining was worth it but at this stage anyone trying to sell USB miners are really just trying to pawn off dated hardware onto someone else.