Deep Freezer (-17deg.C) with auto defrost

It gets down to -30 here during the Winter, and automatically defrosts around May - does that help? ;)

Yes, every frost free one.

However, they are significantly less reliable than non-frost-free ones, as the frost free/defrost mechanism is the least reliable part.

How long does the de-frost cycle take? Presumably the food contents in the freezer are exposed to above freezing temperatures for a while?

Don't know.

No. The evaporator (where the frost collects) is separate from the food, and it's only that which is defrosted. There's no cooling whilst that happens, and it relies on the heat capacity of the food to stay cold.

A quick glace at the temperature logs for my freezer (not frost free) seems to indicate it runs for about 10 minutes, and then takes 50 minutes before it warms up enough to run again. A frost free one defrosts during that idle time (although I don't know if it does it every idle time - I suspect not).