Well, I don't know if I would personally put too much faith in those little locks. I've got several of them lying around the house - they seem to come with
every new firearm these days - and while they will stop a child from doing something very naughty, they don't appear to me to be able to withstand
an adult with even a moderately sized set of cutters. Ruger issued a number of locks with their revolvers back in the early 90s, and while a child could
snap the lock/cable hard enough to spring it open, an adult could, so they were all replaced on a free basis.
A couple of companies sell a "disk-lock" that is basically just a large armored padlock that goes on your front brake rotor. It cannot easily be removed, though
if a robber had a few guys with him and some tools and time, he could just remove the front wheel. Still, it provides good protection against the 'casual' thief.
My major concern with it is like yours with the lock - it is small/unobtrusive enough that it could be easy to forget, and trying to ride off with that thing on would
mean a hugely embarrassing, and somewhat expensive, moment in a parking lot !