curbi can be removed from any managed Apple device. The curbi servers will know about this quickly and let you know that it has happened.
There can be a delay between a bypass attempt and curbi alerting you to this fact. This delay is caused by a device being 'asleep' and therefore not able to be checked by curbi. The actual amount of time a device can operate while bypassing curbi, without being detected is minimal.
This limitation is due to the design of Apple's mobile operating system - iOS.
If you require a more secure solution, consider curbi for Android which cannot be deleted from a managed device.