T-Mobile Family Mode is decent value if you are already on T-Mobile and want network-level controls: it filters content and pauses internet on your kids' lines at the carrier, so it works even when a child switches off Wi-Fi or tries a VPN. As a monitoring tool it does almost nothing — no messages, no app content, no location history worth the name.
What it does well: blocks categories of sites at the network layer, pauses internet access per line, gives a rough location on the map, and sets daily time limits. Because the filtering happens in the carrier core, it cannot be uninstalled by the child — that is the genuine advantage over app-based filters.
What it does badly: the app is slow and dated, location is coarse (tower-based, not GPS), there is no message or social visibility, and it only covers lines on your T-Mobile account. A child on Wi-Fi calling or a different carrier is out of scope.
Cost: it is a per-line monthly add-on; check your plan's current rate, because T-Mobile has changed the price and bundled it into some plans.
Where our app fits. Ultimate Phone Spy runs on Android 4.0+, Windows and macOS (features) and covers messages, call logs, social notifications, installed apps and GPS location on the device itself. The two are complementary: Family Mode blocks at the network, ours shows what happened on the phone. If you want only web filtering, Family Mode is the cheaper call.