I fitted the same topbox to her Enfield a few years back.
Take the nut of the end of the lock barrel and refit with some thread lock.
The one we had was a bugger to open up when than nut fell off and the barrel wouldn't turn the latch.
Other than that a very good budget box.
The Givi I just fitted the my dad's Address 110 is better quality but was twice the price, but there was nothing really wrong with the build quality of the cheap one.