I've been thinking (I know ... dangerous business

) about how to secure the hitch end of a trailer. It strikes me that hitch locks fall into two categories: those which are integral to the hitch, and those with aren't (images of each below).
As I see it there are pros and cons with each type
Integral
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Pro: Compact, can be used to lock trailer onto vehicle
Con: Is security as good as External devices, Less visible
External
------------
Pro: Very visible, security can be validated (e.g. by sold secure)
Con: Seem to only be for use when de-coupled from vehicle
So the questions are ...
Are there any other benefits/disadvantages that I've missed AND Which do you guys prefer?
Cheers
Andrew