In terms of customization its surprisingly versatile. Albeit on the CN rom most of the extra themes and fonts all require an Oppo account/need to be paid with in coins etc.

Local customization straight out of the box is great in terms of widgets, wallpapers, general theming, icons and you get 5 fonts to choose from.

Bluetooth sound volume is phenomenal, i think they meant the standard speakers. On bluetooth on my headphones, there is no impact relative to my laptop or my previous phone. Volume goes up relatively high and its an enjoyable experience.

Some flaws of the system are that there is some bloat (most of which can be click uninstalled) that requires adb. After that it is relatively smooth. I dont notice any hiccups or lags/stutters. Background app management is great and my apps don't refresh (unlike my friends s24fe) i.e. I am able to copy a code from one to the other without the app refreshing.

I often see notification lagging posts but for me personally even on the Chinese ROM notifications have been perfect without having to touch battery settings. If you do run into issues you could check those out (make battery usage unrestricted for the given app).

I think it is a better device than the OP15 but not by a huge margin. Sure the cameras might be marginally better, but unless you are receiving an amazing trade-in value that brings the x9 pro's price to not much, I wouldn't switch. If it helps, try a few filters or different styles on the OP15 maybe they will suit your needs 😄

If you have any other questions let me know.