I browsed all kinds of options before my Dad recommended this from the shortlist I presented him with. It is flexible (even more so in hot weather) and thus locks well onto lamp posts, railings and even thicker objects which a U-lock wouldn't latch on to. The slot to protect the mechanism from the rain is useful too.
One can only remove one's keys from the lock once the mechanism is closed, something I hadn't come across before. But this is by no means a problem, just a word of advice in case you try and yank your keys out and thus break the lock.
Would thoroughly recommend.