buying a used kncminer Jupiter

[1giantrobot]

I'm considering buying a used Jupiter that is for sale.  I would like to avoid problems and I'm hoping some folks with experience can point out any issues I might have. 
The first question is simple: Is there any obvious reason I shouldn't buy it?  I've run the numbers on the genesis block and should be able to turn a profit based on what I'm paying for the miner, barring a price crash.
What are some other things I should consider?
Thanks.

[cunixion]

allow for 1000Watts power requirements.

[mjc]

Here is a simple formula to use.

How many BTC will you have if you buy Bitcoins today with the same amount of money?

How many Bitcoins can you earn with the miner?

If equal buy Bitcoins .

If fewer by mining buy Bitcoins .

If more with mining and you are confident in the values you used when estimating, then consider buying the mining equipment.

For more check out my blog: http://bitcoinsbs.wordpress.com/2013/12/13/do-i-mine-or-not/

[4chanme]

you should invest into something better

[stompix]

you should invest into something better

Define better?
What did you compare , so you think something is better that the offer he has ?
He didn't even mentioned the price!!!!