At BTC, you'll pay for it in about a month. That's their point - that it's unreasonable to expect units to be priced at a point where they'll pay for themselves in days. They're leaving themselves plenty of room to adjust the price downwards as difficulty changes and more TH hit the network. There's only going to be a short time when expecting a unit to pay for itself within a couple of months is reasonable. As more ASICs hit the network, the break even point will blow out. When it blows out to a point where sales drop off, vendors will likely drop their prices to keep it at an "acceptable" time-frame.
The point that the vendor conveniently eschews is that it was not his capital that paid for this development. Sorta like
skepsidyne rehashed, or in other words never trust a Bitcoin miner. (That link is instructive of the entire "capital doesn't matter" attitude of miner folk, by the way).
In practical terms, the hash rate is ~50 Gh currently, even if units were delivered normally you'd be paying 100 BTC for 0.1% of current hash output, which means you'd be even in roughly a month if hash output stays put and your electricity is free. That sort of deal isn't interesting at all, let the very "
ethical" ngzhang run his own rigs to his heart's content.
Which brings to the fore the following issue: two Chinese brothers were born the same day. One, AbelMiner, came to the community, took 20k BTC worth of equity which was called equity, built miners, faced all sorts of challenges, troubles and problems but eventually got about 6 Gh online. The other, Caivalon, came to the community, took 20k BTC worth of equity which was called "pre-orders", built miners, faced all sorts of challenges, troubles and problems but eventually delivered about 6 Gh worth of units to shareholders and then walked away from the deal under the guise of a broken pricing model.
Granted, this isn't quite as much of a scam as BFL. It's more of a scam than Asicminer (at least so far) and I would say on the scale these things are normally judged it counts as a scam. That the sheeple aren't quite immediately aware this is the case...well...this is how Bitcoin mining "ventures" go, isn't it? Gigavps launched bonds, paid 3-40 cents to the coin to date (but you can dilute that if you wish to "upgrade", of course); hashking launched "investments", paid 30 cents or less; amazingrando idem, this is the story since day one.
Eventually the sort of people that go for these sorts of deals will run out of Bitcoin. Sometime in 2050 or whatever.