Nick, I could never see the point of the Velo-vice; you have to take the front wheel off, secure the forks in the mounts and then put the wheel in the boot (or on a carrier). With my 510s (forgot the number ...), I can throw the bike up and secure it in seconds. Apart from those points you have mentioned, why would you choose a Velo-vice over a 510/591? Just curious ...
How could you (or someone else

) forget to do up the latch?

I am
so anal about checking the security of the rack. Good tug on each side, make sure all the locks are locked, tug on the bikes, look up through the windscreen to make sure they're still there

, etc, etc.