I don't leave my bike unattended and out of sight for any amount of time-- save for when it's on the rack on the back of the car, and in that case, it's Kryptonite U-Lock and a 15' cable combining to look like my bike is being attacked by a hydra.
When I'm out on a long solo day and I know I might have to make a stop to use the restroom or to grab a snack, I use a Knog Milkman. It's small enough to fit in a jersey pocket, and acts as the little bit of "stop someone from just walking away with it" security.
That's how I view locks like the Ottolock. And that applies to pretty much any lock under 2lbs, really. Security is heavy.
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