Totally agree -- this platform looks very cool -- the deposit approach is pretty elegant.
The deposit approach *is* elegant but there is a bootstrapping issue with it. If the fiat currency holder has only fiat currency and *no* bitcoins then he can't put up the bitcoin deposit to start the Coinffeine-based exchange which he wants to carry out in order to get bitcoins. :-(
I agree. If you are going to an exchange to purchase bitcoins and have no bitcoins yourself. How do you put up the deposit?
The amount you can buy is proportional to the amount of bitcoin you have. In principle, with very small initial amounts you can initiate a series of exponentially bigger exchanges. You can find those initial amounts from sources like faucets and, the authors of Coinffeine are considering different ways of providing this small amounts.
BTW, I'm one of the developers