I know this will probably be controversial … but …
If you cannot trust your kids with a phone then they should not have a phone not just a tracking app on their phone.
You are demonstrating you don’t trust them about everything … not just the phone. The phone then becomes just a symbol of the lack of trust. Safety is just a rationalization. If you cannot trust them to be safe because somehow their judgement is flawed that is a problem … not a phone problem … which is the fault of the parent for not coaching and teaching good judgement. Yes there are exceptions … but those should be moments to teach them about judgement even when you have to draw the line. And also yes … teaching good judgment in all cases before they develop is a formidable task. That is why you are the parent and they are the child. You have the experience.
Trust is a two way street. If you demonstrate trust it is likely they will reciprocate.
I firmly believe you should teach your kids to do the right thing when you are present and when you are not. If you simply try to put them in a “box” to control their behavior you will erode trust and eventually they will break the rules by being very covert when they are temporarily outside of the “box”. When that happens you have lost control. Ultimately the relationship will be damaged because the child will feel they have been forced to lie for the occasions they covertly break a rule. And lying never improves a relationship.
If you do have a strong trust relationship it is likely the child will occasionally stray outside of the lines you hope they would stay inside as part of a normal learning as they mature. If they have learned their lessons well then they should “self check” and correct their own behavior … and hopefully think “mom/dad you were right”. They may not say it but you will probably feel it.
Just one persons opinion.