An all metal lock nut would be more suitable, as the nylon insert has temperature limits, which can degrade the nylon properties enough to reduce it's inherent friction. Usually the limit is about 250F. Sometimes these fasteners are accidentally used close to high temperature components, such as exhaust manifolds and down pipes. Not a desirable thing to do.
Also remember that the lock nut friction reduces the actual induced (compared to the desired value) fastener/bolt tension or clamping force when tightening. This should be taken into account for mountings which call for specific torque values when tightening. The trick of course is to get it correct. Industry does this by using methods such as clamping force measurement washers.