(hope 2 months since last post isn't much)
Another note: for some time(since Juha's last post on this thread) I've been trying to pick the U-lock with various ballpoint pens, to test its security. But, much to my surprise, I failed every time. The pen barrel would crack upon attempting to open the lock with it. On several occasions, chunks of plastic from the pen apparently remained stuck in the locking mechanism; fortunately I was able to remove them with my fingernails, and the lock hasn't been damaged.
Then, I found out that not all tubular pin tumblers can be picked with a pen. Up, to now, it seems like mine isn't that vulnerable. I was wrong to give it up before testing it.