Abus Mini U-Locks
Abus locks is a classic example of German engineering, with over 80 years experience making locks, and some 50 years making bicycle specific lock mechanisms. As in, Abus had a u-lock on the market back when my parents were learning to ride on two wheels. At left is the $90 Granit Futura, a remarkably light mini u-lock at just 720 g with a high security rating, on par with other mini u-locks on the market at a significant weight savings. The shackle is a lightweight hardened steel alloy with the lock mechanism engaging both sides of the shackle, making it resistant to twisting and prying attacks, along with being near impossible to cut with anything but power tools in any sort of reasonable amount of time. The lock ships with two keys and a unique key code, allowing the end user to purchase replacement keys and order other Abus locks with the same key, making locking up that much easier. Two of these locks (one for the frame and rear wheel, one for the front wheel) would do a good job of keeping your bike yours in even the most theft prone cities.
The red U-Mini is a more affordable option at $65, with a bit beefier of a shackle and an extra 200 g or so of weight. The lower price point means that this lock is not compatible with the previously mentioned Abus key program, but that doens’t mean the lock mechanism itself is any less effective. This lock is less tech and more brute theft resistance through thick steel and the pick resistant key mech.