Please don't spread FUD! Make a good research 'what it was'!
He is going away from the truth. What it was is: Mt.Gox's GreenAddress is different from this. They created their own not they supported this wallet. This wallet was released after Mt. Gox was shutdown/hacked and how could they support this even before the release? It is safe to use GreenAddress as it provode signed time locked TX which you can use to get your coins after the lock is expired. You can do 1 day trial or you can also use their testnet wallet before using mainnet if you like.
Edit: 'Green address' like style was first implemented in Instawallet. See the ANN: https://bitcointalksearch.org/topic/instawallet-introduces-new-approach-to-instant-payment-green-address-technique-32818 and then in Mt. Gox, ANN: https://bitcointalksearch.org/topic/mtgox-green-address-option-48170.
-MZ