Orbi RBR 50 router firmware - 2.7.4.24 or 2.7.5.4?

They are both "right".

When Netgear first releases a new firmware update, it appears on the support web site, where Early Adopters can discover it, download it, and experience "what happens".  (Parables about "Fools rush in, where angels..." come to mind.)  There have been a number of embarrassing situations where new firmware causes unexpected problems. Obviously, the Quality Assurance tests cannot catch everything.

After the new firmware has been available for some time (perhaps 4-5 weeks, Netgear will "flip a switch" (not physically, but logically) and Orbi's around the world will notice that "New Firmware is Available" when they check in (every night --- every single night!)  This appears to be rolled out in stages.  If the user happens to notice, then that new firmware can be installed.

At some further date, Netgear decides, "enough already." and pushes the new firmware to routers, again in a staged fashion.

There are, after all, customers who never look at the Orbi app or open the Orbi web interface.  They bought the system to user it, not fool with it!

So, yes, both are "right".  Feel free to download and install it.  v2.7.5.4 has been on my RBR50 since March 15.  I waited about three weeks after it came out, saw no "the sky is falling" reports, and took the plunge.  So far, so good.