those look great...
but, if you are going to be leaving those on the vehicle and parking out in public, i would suggest some security measures. looks like the actual rack has locks. that is a lock tumbler behing a rubber cap?
but, i would do something like getting a couple coated nuts of the appropiate size and putting them on the threaded rod that the knob for tightening the clamps is mounted.
using them as jam nuts will go a long way towards keeping the honest honest, and reduce the 'opportunity' of a crime of opportunity.