my 20 cents on the topic of Funtouch vs Origin, i think really depends one. OriginOS to me is more customisable, has more features, UI is much much nicer, way more granular control over app permissions, ability to remove most preinstalled apps... But then it's a China only OS, so it's crapshoot when it comes to whether it will play nice with all the apps you need. For some it will work, for some might have deal breakers.
Like with OriginOS 4 which i used for 4-5 months here in SG, mostly okay, but just telegram text input field will turn transparent from time to time (need use telegram x). OriginOS 5 seems to be okay with that, but then apps like DBS/POSB will always force close on a fresh launch. 2nd launch or when still in recent apps, then no issue. GPay with DBS/POSB card didn't work for me too, though this one i think not unique to originOS and not an issue for me since I use other banks for GPay anyway. Then OriginOS still won't play nice with apps that uses persistent lock screen notification, like Adidas Running. I am not be able to get it to show up tracking activities on lock screen at all.
Then you have games, which won't be able to take full advantage of all gaming features like frame interpolation, resolution upscaling, etc since apps has to be whitelisted. like genshin global client won't have frame interpolation at all, need to be running genshin china client then can. the most funny is iqoo neo10 for me. in Genshin and honkai star rail, if i turn off the all brightness high PWM dimming so that will use DC-like dimming for higher brightness, those 2 games FPS will be limited to 50FPS for some reason, and i think only for global version of the game. best part is... even with all brightness high PWM dimming off, once you open a game, the screen goes back to high frequency PWM dimming anyway (same for 2 other iqoo phones I've tested with originOS 5 by the way, not sure about funtouchOS 5). for me i'm very sensitive to PWM dimming these days and also play games, so for me, even though i like OriginOS, probably won't be able to use their phones again until i know they change this behaviour. but on the other hand, for those not sensitive, or don't game, this won't matter at all.
a lot of this are things you won't really know until you really use the phone with the apps you need. i know the general consensus when looking at a lot of reviews from China side is that OriginOS is really good, but have to factor in that they are using the phone in China, which will naturally have way better compatibility. so basically, if interested and curious, just ownself buy and test. if suitable and no deal breakers for you, then great, get to save some money too.
For FuntouchOS 4 when I use on iQOO 12 a long time back was more stable and feels like got less small issues here and there... but i feel like that's also because the OS has a lot less customisation options, less features (especially those integrated into china specific services), and because it's made for global market after all. so like gaming related features they'll whitelist global clients, so better compatibility for global apps/games. but not sure how it is on FuntouchOS 5, but on 4, they don't allow removal of some bloat which is annoying. then got that Jovi button in the quick settings pull down menu at the top right corner which die die they don't let you remove on funtouchOS 4 (super annoying since that location is where most other android phones will put their "Settings" shortcut), don't know if they allow removing it on funtouchOS 5 or not. personally, really don't like the way it looks too, and funtouchOS4 felt noticeable less smooth/fluid compared to originOS4. but the things that annoying me some people might not care about, and will prioritise better global compatibility and a more "stock" looking UI. basically YMMV. ¯\_(ツ)_/¯