One problem with using a location for a task in Reminders is that you can only select a location from your contacts list. You can’t select a location on a map or enter in an address. I’ll submit a feature request if I get time.
Also, even though there is probably not a better way to do this, the Reminders app uses your location continuously if you have a location based alert set up. It appears to check roughly every minute with low accuracy.
Yesterday, I was across town ~ 5 miles from the location of one of my tasks and it alerted me twice in a row.