Well - CEX.io works for me - and I'm grateful for what they offer.

To be able to buy and sell Ghs instantly offers a whole new dynamic to mining, which is a mixture of the trading exhanges and mining at the same time.

Yes - Just buying to mine will likely not make roi - but buying and selling and mining while the price is stable is an excellent way of fighting the depreciation of mining hardware.

As with everything - you make your choices, but as CEX,io is not just about mining - it would be misleading to write it off on that basis alone.