That advice predates the battery-powered angle grinder, which many bike thieves in Western Europe now use. Even the toughest, most expensive U-lock can be broken in about a minute with an angle grinder.
2 locks is indeed the standard in big cities. Also make sure they are sold secure gold rated or Art 3. Anything else is a waste of money. There are a few new lock types which are supposed to work better against angle grinders like Tex-lock or LitLok.
Because the average bike price is going up it also becomes interesting to steal parts. A decent handlebar + shifters are easy to sell individually. Companys like Hexlox or Pinheads are working on locks to tackle that.
That's an interesting point. Doesn't that make a folding full-size bike the only real solution?
Something like Changebike DF-611MB:
https://www.changebike.com/df-611mb
> There are a few new lock types which are supposed to work better against angle grinders like Tex-lock or LitLok.
After a quick search...
Tex-lock cut in 32 seconds:
https://www.youtube.com/watch?v=ictBpMHKhK0&t=1m20s
LitLok cut in 16 seconds:
Presumably if it's actually his bike, he'll be thankful.
Of course, my confidence to do so was buoyed by the fact there were two other bikers parking at the same time as me, it was in a busy public area, and I was wearing a bunch of leather and kevlar.