What doesn't work ?

Fair question.

I expect the following from such a system : I set a time limit per app/set of apps,and the phone locks said apps once the limit is reached. In theory, this is what it does, in practice it almost never works : it doesn’t lock, gets broken whenever you upgrade the os, gets broken whenever your child upgrades the os, can be trivially bypassed by a kid, cannot be unlocked when you want it to unlock remotely etc I’ve also seen trivially bad data ( phone usage when it was in my pocket ). It’s worth noting you also need an Idevice to set it remotely - if your significant other has an android device he or she is out of luck.

I was very surprised at how appallingly bad it was - just try it for a few weeks and you’ll immediately notice it’s badly broken but somehow doesn’t fix it.

Contrast this to google’s system which, well, works.

Edit : it’s so mind bogglingly bad that I’m genuinely curious to talk to someone who works at apple about this.