How effective are DIN 985 self-locking nuts?
In the General Aviation aircraft industry, AN365 / MS20365 full-profile Nylon insert self-locking nuts are an important staple. Use them with the appropriate washer and in appropriate locations.

Nylon insert self-locking nuts major weakness is heat, they are recommended to only be used in areas that never exceed 250°F (~121°C). The heat softens the Nylon, reducing its gripping power. 

For high temperature use, metal construction self-locking nuts are used. Nylon is a little more gentle on the threads, the full metal nuts either have one end ovaled or have the end castellated and compressed to grip the threads and can be like running a thread cutting die on the bolt if disassembled multiple times.

Straked Top Lock, Nylon Insert, Torque Nut