From their FAQ page[0],

    What happens if the string snaps?

    It takes 10 minutes to replace, by the rider. No specialist knowledge required, worth watching the tutorial on the website. No tool required, no need to remove the rear wheel, or other parts. Spare string is provided, and neatly stored in the seat pole. The spare comes with instructions to install.

0: https://www.stringbike.com/stringbike_support_questionsandan...

I like this stringbike, if I needed a bike currently I would consider it. However, the durability while minor is an issue. I have never had a chain-link snap. I have frequently had chains derail. So the metric in my mind is, how frequently does this method need maintenance, replacement or derailment.

It looks like they're juuuuuuuuuust the right length so they perfectly match up to pedal stroke.

i.e. - Your push stroke unwinds the string to its max extension length, and then the rotational inertia of the wheel does the job of winding the string up again.

EDIT: Scratch that, disregard the above. Looks like they're using a spring to wind up one side while it freewheels.

As for assholes? Yeah, they're going to be able to slice those with a pocket knife in a few seconds. Even Dyneema and the like would likely be quickly frayed with a few good knife swipes to the point of being in danger of snapping from a hard pedal push when taking off from a stoplight.

An interesting security feature would be if you could take the string with you whenever you dismount. The site says replacing the string takes "10 minutes" though, which is way too long for that.

regular bikes are also vulnerable to pocket knives