I would not give them any money until they prove those machines exist.
It is a gamble for sure, but if you wait until there is proof that they exist, it is already too late. There will be too many orders in front of you and by the time you get your miner, it will not be profitable any more. Butterfly Labs orders ran into the same problem. I ordered my Jalapeno late and it took 6 months to get it. Now I'm only getting ~0.004 BTC per day with it, having spent ~$170 on the miner. It will take a while to pay for itself at that rate.