EMS is trackable from ParcelForce once it arrives in the UK as you know. The seller may not see any detailed updates on his or her Malaysian EMS tracking site once it is handed over to ParcelForce.
EMS has insurance available ( at increasing cost ) for up to US$20,000 from memory. In my experience customs interest regardless of carrier or what's written on the papers ( "horological item" / "item for repair" / any other internet WIS legend ) appears to remain a lottery. For the insurance to be valid though, the full value of the goods and an accurate description must be entered on the EMS form.
I have recently been asked to explicitly declare on the description whether the watch has a lithium battery or not when sending to the USA due to new rules, so things do change from time to time.
Paul