Apple specify the weight of the latest 21.5" model at 8.8kg. I am not sure if this includes packaging and accessories.

I have yet to experience over-zealous hand baggage scrutiny at DXB, but reports indicate that it does happen with some regularity. All those cashiers near the check-in desks need to be kept busy somehow.

If placing in checked baggage, I find the greatest risks are due to crushing should your item be loaded first into the hold or container and heavy items with rigid edges thrown on top. I would pack in original box, then pack that in a larger box or suitcase with a few inches of padding/packing in all directions.

Placing the original box inside a bin liner first (to protect from moisture) may seem excessive given that baggage is rarely left outside in the rain. However, after a recent flight where every second passenger was carrying 10 litres of poorly packaged holy water, I would recommend it! My bag escaped, but some others were drenched.