I upgraded my N10 to 11, and it's occasionally less "smooth" than before. 10 was awesome, no issues. 11 is not a deal-breaker, it doesn't lag all that often, and it was more noticeable right after the upgrade. Not as much anymore, it's subtle but there was definitely a difference.
As for as UI changes, it didn't add anything useful for me. Any Oxygen OS nicities over stock we're already in 10 for me. And I agree with the 4a preference above. I was in Hawaii in June when I sadly drowned my 4a, and my N10 ended up being the vacation replacement. The 4a takes better pics in different conditions, although the N10 camera isn't bad, just not as good. With that said, the N10 is a great device. SD card, 90 Hz screen (albeit LCD instead of OLED), 5G, 3.5 mm jack, and a great price.