Having bought quite a number of items from APUG sellers (all but 1 in the US the other in Israel) I can honestly say that it's as easy buying from the US as the UK, items arrive usually within a week, shipping not too bad unless you're buyin a 10x8 camera
Prices are very significantly lower, I'd snap this Rollei up if I had spare cash, hang the no shipping outside the US, I'd get it shipped to another US member and then re-shipped, fully insured, tracked etc.
That doesn't maen I haven't had problems, I have twice, once the seller never shipped kept promising anmd with help from a moderator also stung by the same person I eventually got my money back.
The second item never arrived, but because I had faith in the seller I/we waited patiently with excellent communications & trust between us, the item was returned to him months later by the post as uncollected (here in Turkey) and I received it with no glitches 2nd attempt this time to the UK.
It is about trust, using the right form of postage, as a buyer not wanting the cheapest option unless your prepared to accept a risk. The onus is at least that the seller can provide proof of postage but I'd expect this in a UK/UK or US/US transactions s well.