I would like to go out on a limb here and say that the whole world should use DIN rail mount equipment.
It is so simple to work with, I mean unless you are dealing with an elderly building that still has HRC fuses or what-not, tear it out and use metric DIN rail stuff.
You can work live on DIN rail stuff, simple as, all the breakers are the same physical size, apart from the width for multi-phase circuits.
No connection issues, just do your terminals up tight and you're done.
Actually that isn't quite true. As soon as you get to bus bars you're back to type testing and only combining parts from the same manufacturer. Neither the height of devices nor the distance between the terminals and the front of the device are completely standardised, so you can be a few mm off, enough to cause overheating under high load. UK manufacturers also have a whole range of completely incompatible RCBOs that are much taller than standard MCBs, requiring much larger enclosures.
Apart from that I think the great thing with DIN rails is the sheer variety of available devices - MCBs, RCDs, relays, contactors, switches, dimmers, sockets, motor relays, doorbell transformers, doorbells, bus actors, you name it!
And you can always get around the issue with type testing by using wire links in a pinch (replacing an old MCB or RCD that's no longer available).
