A huge amount of software collects data by default, because accounts and analytics are the easiest way to build a business. Halo was built the other way round on purpose.
No account, because there's no need for one
There's no sign-in, no password to lose, no account to recover. Opening the app for the first time means naming a pet and starting, not creating a profile and confirming an email address for something that has nothing to do with anyone else.
No ads, because that's not the trade being made
Halo doesn't run ads, and never has. An app holding someone's pet's health records showing ads alongside them was never something worth building.
No data collection, because a medical record isn't a product
Every medication, weight entry, and note stays on-device and in your own private iCloud, not on a server anywhere else. There's no analytics pipeline reading what's actually in a pet's medical history, because that information was never the point of building this, helping you track it was.
Why it matters more for something like this
A to-do list app collecting usage data is a fairly low-stakes trade. A record of a pet's ongoing heart condition, medication schedule, and vet history is a different kind of information entirely, and it deserved a different kind of default.
Halo was built around that decision from the very first line of code, not added on afterward as a privacy policy.