How does the Buckley differ from the Boston clog?

Both use the cork-latex footbed and an open back. The Buckley has a suede upper with a side buckle and a softer, more shoe-like shape; the Boston is a plainer, wider clog.

Is the narrow width much slimmer than regular?

Yes. Birkenstock's narrow fit is noticeably slimmer through the arch and forefoot. If you wear regular-width Birkenstocks comfortably, this pair will likely feel tight.

Do I need to break them in?

Expect a firm footbed for the first week or two. The cork and suede soften with wear, and many owners say they become comfortable after that.

Can I wear them outside in wet weather?

The EVA sole handles pavement, but suede and cork do not like rain. Treat the suede and avoid puddles to keep them looking new.

How should I size them?

Birkenstock uses EU sizing, and the size menu lists the US equivalent. The open back gives some room, but the narrow width means you should not size down.