I use CR with iPads, including retina and MBPs. It works very well. It is easy to determine accurate focus as are looking at a jpeg (transferring captured RAWs is to time consuming) on a larger screen that you can zoom, but other advantages are:
- Larger screen footprint makes it easier to judge composition, lighting, etc., when tethering RAW into laptop, etc., just not practical
- You have a larger screen (vs camera) that is still smallish and mobile - can setup to your side or low on groudn with you, etc, so can just shift eye(s) over & glance at between sequences w/o chimping camera LCD
- You allow others (especially using CR Share) to see or just or see/rate/comment on images and give you feedback w/o having to show them camera rear if laptop usage not prudent.
- Full camera control from iPad/phone/laptop if desired.