As Bjornorn writes down tube are mostly stretched. Some bikes just use a wire. Incidently that could also make for a better locking system that the stiff one with cuts.

https://www.designboom.com/technology/kibisi-biomega-bos-8-s...

(1) was my first thought, especially on that part of the frame. i think if it was the horizontal upper bar, it would be less of a concern, because the upper bar gets different stresses.

also, this lock is way to bulky for many locking situations. i can't even think of a bike-rack where this would work. it seems to be suitable for locking to sign-posts only. (and see the comment below on that)

Ritchey sells breakaway frames for easier transport, and their frames are definitely not weak, so I would say no.

I've never had a breakaway bike, but judging from photos the Ritchey couplings look a lot sturdier than these hinges.

It's probably still ridable because the top tube is rigid, and for a bike that's mainly geared at convenience stiffness isn't a priority anyway.

> (3) Once LPL shows how to open that lock, one might want to swap it for a better one. Is that possible?

Looks like a disc detainer lock. Possibly needs "A pick Bosnian Bill and He made", but as we all know, there are disc detainer locks and disc detainer locks.

I'm not sure it's a top of the line, high security cylinder. Hope it's replaceable.

Nobody actually picks disc detainer locks to steal bikes. Even crap ones.

Bolt cutters or angle grinders are faster and easier.

The downtube is mostly subjected to stretching forces. But maybe it does lose some stiffness compared to a normal bike.

Using a wire, at least, makes it less stiff in torsion since a regular «metal tube» will have bending and shear stiffness. But then, it’s a tradeoff which could be worth it for some casual bikers!