This is a U-lock from SAIKO. It locks the wheels of motorcycles and bicycles to prevent theft. I think it offers high security because it can't be easily cut like a chain (though it doesn't guarantee 100% prevention). It only has one key. I haven't used it much because it's cumbersome to carry, but I think I bought it over 10 years ago. There are scratches on the protective cover from when I dropped it. See the 5th image. I have confirmed that it works. Please refer to the images for the condition and length.