The location alert is using Apple’s geofencing API,  utilizing the cellular antenna fix rather than using the GPS component (this is the reason that the iPad has to be GSM for this feature to be available).

Since the GPS is not used for positioning, the battery consumption should be almost the same, with or without a task with location alert.

You may also notice that the location icon appeared at the top toolbar is outlined (not filled), which means that the geo-fencing is active.

You can read more on your device’s Settings > Privacy > Location Services, scroll to the bottom.