How do the prices work? Do they rapidly fluctuate with the price of bitcoin, or are they fairly stable?
Unless they rapidly fluctuate the shop might end out undercharging and losing profits, or overcharging, depending on if bitcoin has rapidly gained or lost value.
+1 on the bold part.
I think the price adjust its self with the market yes.
Have you used the service yet?
I notice they even sell perishable goods like bread. Most normal supermarkets offer a delivery service nowadays, but this is even better because you can pay with a range of alts.
One of the first things I notice was they sell e-cigarettes. Those should be a popular product. Everywhere I go someone seems to be "smoking" those things.
No i haven't. Don't live in the UK unfortunately, but we have some peeps on our Reddit who is going to try it out http://www.reddit.com/r/QuarkCoin/comments/21oovt/from_the_uk_pay_for_life_essentials_with_quark_we/cgf1zis