...A few points of clarification:
* RCD's can be breakers or outlets (there are a few other specialized devices out there too, but most people won't encounter them). In the US the term GFCI is much more common, but means the same thing: A device that detects and reacts to an imbalance in current.
* RCBO's are RCD's that also include overcurrent protection. Thus GFCI outlets are RCD's, but GCFI breakers are RCBO's.
* This thread has been discussing breakers, not outlets.
* GFCI outlets (usually) have a separate connection for an earth reference because three-wire appliances expect an earth reference. GFCI breakers typically do not have a (fourth) connection for an earth reference, at least not in the US. The third connection on GFCI breakers is a (usually white) pigtail that is to be connected to neutral, without regard to whether neutral is bonded locally or distantly to an earth reference. A GCFI breaker is therefore designed to function properly with, or without, a bond between neutral and an earth reference...
AFAIK RCBOs here in Australia/NZ and the UK are a combination of RCD and MCB combined, usually in a single DIN slot package with active and neutral from the N busbar coming in,
and active and neutral going out to the load/s.
The RCD section work as they should to spec and easy to verify with a decent RCD tester
The MCB section, depending on the current curve (B, C, D, or anyone's guess sometimes..

) reacts to short circuits and massive 5x > 10x current draw,
but a bit of a fail on slow-ish thermal based gradual over-current.
The 10 amp rated small breakers fitted to 4 way/6 way power boards/power strips work a lot better in that regard,
once things get ~hot~ anywhere from 8 amps to 20 amps, they will pop reliably,
whilst the 16 or 20 amp RCBO downstream fed with warm wire symptoms just sits there clueless
fwiw I use RCBO and power strip to cover all bases,
and if I need a faster and or no brainer solution, a temporary in-line fuse to suit the load or DUT

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How does the GFCI thing work with 120 and 240 volts over in the US?
Do the separate 120 and 240 circuits have separate rated GFCIs, or go to a Master?
What about 208v branches?
I've seen Youtubers play with 120 <> 240 adapters to pull serious welder current or power homebrew -LightNing- rigs
are they still getting GFCI benefits if GFCI is fitted?
Will GFCIs in the US still work with a good centre tapped Neutral connection and failed Earth connection
and how reliably?
More better worded questions coming once the coffee kicks in..