I'm thinking about purchasing an antminer s5 does anyone know how good they are.
Personally, this is the worst miner that I ever had. I am constantly bugged with. Whenever I have an internet problem or that the pool has a cut, I do not know if they will restart themself. Sometimes you have to cut and then restore power to that they restart. And sometimes you loose an hashboard...
Those selling them want too much money. And be careful that they are stable.
Remember that 1S7 = 4x S5. If you are offered the S5 @ $ 150, it is equivalent to the price of a new S7 which consume half of electricity. The choice is quickly made in this case...
Edit:
Read carefully talks_cheep and vero, they are right.
And in addition be very careful when buying a miner. there are a lot of scammers trying to sold outdated equipment at a high price.
Mining activity is valid only if you have the very cheap electricity (all the time).