John Rumm wrote:

No they switch both live and neutral

Not necessarily, and most are single-pole switched.

- the neutral of the circuit has to pass through them as well as the
live (makes sense when you think how they work). So they switch
both.

That's a non-sequitur. Just because the neutral passes through doesn't
necessarily mean it's switched.

Both single- and double-pole switched RCBOs are available. Generally
speaking 2-module width ones are DP and 1-module width ones are SP,
although that rule might not hold universally. Manufacturers'
literature should make the situation clear though.

--
Andy