MyGHL is much different than the IPhone app. the IPhone app really is more of a 'status' app than anything else (you can do simple tasks). Can't acknowledge and rest alarms, for instance.
MyGHL offers nearly 100% control. That being said if I was setting up a tablet to run either MyGHL or the client, I'd just do the client (assuming you are using a windows tablet). Otherwise, yeah MyGHL.