For my Pi's I buy a separate RTC (uses GPIO pins). There's various available, the DS3231 is the most expensive but also the best. If you buy it in bulk (70+) I suppose you could shave some money off. If you're OK with a cheaper one (less than half the price) which functions less well (but still does the job) then PCF8523. I got mine from a local Adafruit reseller.
We couldn't justify adding ~$2500 to the bottom line, but you can be confident that we sure did argue about it.
I'd say 50/50 that I didn't know what I2C was in 2014.
Still, if we had gone and designed our own RTC daughterboard, it would have replaced the UBEC in our architecture diagram. We were buying those for $3-4 in 1000 unit quantities.
So, had you been on hand a decade ago, you might have won the argument although if I put on my board member hat, fabbing our own PCB sounds a lot scarier than buying boxes of buck converters.
It's hard to express how wild it is that they just pop right on and guarantee close to perfect voltage to each device.
https://www.alibaba.com/product-detail/UBEC-5V-3A-5A-7A-15A_...
From your URL, the second part made me wonder if the statement is correct: "UBEC 5V 3A/5A/7A/15A BEC 2-12S Lipo Step-down Module External Power Supply Full Shielding Antijamming For FPV Airplane" would this actually work?
And now, you too can share in the late night cackling joy we experienced so many years ago.
Those three pin headers on the UBEC just glide right into place on the +5/GND pins at the top of GPIO row.
Note that the graphic animation also explains that this UBEC is certified unisex... so make of that what you will.