You're missing the point. Apple set these appointments up simply as a courtesy because they know it will be a big crowd of customers swarming the stores to buy one. They appointments are only 15 minutes. Have you ever worked in retail? Customers take much longer than necessary. Allowing them to switch bands will slow everything down and other customers will get pissed. Some control has to take place.
So what happens when a customer inevitably can't decide between three different bands? According to the post on 9to5Mac a few hours ago, you get to choose two watch models to try on. If someone goes into the store wanting to see how the link bracelet, milanese loop, and leather loop look on them to determine which one they want to buy, they're forced to forget about one of them. This is acceptable marketing for a company like Apple?
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What combination is Apple not offering that you need to try on to know if you want it?
Personally, I'd like to see how the Space Black Stainless Steel watch looks with black and white sport bands.