At least in my experience the big lock is an effective deterrent. I have had regular low end u bolt locks cut and commuter bikes stolen several times. Once I had to.ride my nice bike to work for a couple hours, and brought my big heavy kryptonite chain thing. A couple other bikes were stolen that day but mine remained. It may have been luck but it never hurts to have the more difficult target. in a high traffic area… (Although nothing would have helped that day the thieves just stole a whole bike rack…)
One day when I get a new commuter bike (seriously buying bikes now is hard) I’m going to try the “ugly it up” approach too.
