With my currently Y7 DD who has a cheap argos phone, the benefits have been:
-- she has her bus ticket on her phone (to me this is more neutral, but she says it's much better than the paper one she used to have).
-- she can access homework via the Teams app though as I've blocked the internet browser on her phone she has to use a computer with me if there is a link
-- she's used Duo and texting to talk to her friends
-- she loves the drawing and 'paint' apps, she finds it really soothing and stims with it when she needs to chill out.
-- I sometimes get random sweet texts.
The cons have been
-- the expense, though some places do family discounts. I have 5 of us for about £34 a month, but we're a family that uses very little data.
-- as her school doesn't use mobiles during lessons unless at home, she always has it on do not disturb so when she misplaces it, it's a whole thing until I remind them to double call it.
-- She does get distracted with with the drawing apps and music on it, though I've a tight lock on screen time so she only gets an hour a day for that unless her father or I add in extra time. I think this has helped. Her Y9 sister is more distracted with it, I swear that child can teleport to her room to go dancing with it the second my back is turned.
After using a few apps (and a few bumps with DS1), we use Google Family Link for screen time and controlling/monitoring apps. All of the kids, and even their father, leaves their phone downstairs at bedtime, always have. I think creating routines and expectations around them is really important (though sometimes very hard to stick to).
she can't bear kissing in films so she's not heading for porn sites or anything like that
My DS1 used to leave the room when there was kissing on TV, and once ran out of the room when his sister asked about where babies came from and yeah, at 13, he had an error that he asked my help on which ended up being caused by his phone having too many Deviant Art windows open and we had to have a bit of a chat on that. The next
6 months were a roller coaster of internet related drama - mostly around violent graphic novels - which is why the younger ones have internet browsers blocked on their phone (as did he, at his own request, until he was 15 as he found it all too easy and tempting).
I'm not saying your DD will have anything similar, but my boy taught me that showing a disinclination doesn't stop the internet rabbit hole of curiosity so anything along the lines of how uninterested a child is makes my brain scramble. I wish I'd blocked the browser sooner rather than thinking that being in the same room with a child who had at most shown annoyance for that type of content had been enough.