So I'm aware that if anyone really wants my bike, they'll be able to break through whatever I have it locked up with if they have the right tools... Currently I just use a combo cable lock, which is plenty for where I live (almost overkill really). I was thinking of getting a U-lock for city riding, and using both locks together. It looks like the combo u-locks are generally cheaper than the keyed ones, is this because they're less secure?