I think they are great for the non-commercial pilot flying a Cessna 182, or the like. I recently acquired an iPad 2 and moved one of my JeppView allowances to it. It's good, but not as good as my 27 inch HP display on my desktop. And, not as good as the chart display I saw at Honeywell for the Falcon jets.
The problem being you have to scroll the chart to see all of it at a decent scale. Not so with the industrial strength built-in stuff.
Cesnna 182 flying, yes; Boeing 737; no.
The same could be said of the time it takes to dig out a chart then open it up, find what you are looking for then fold it so that it is not cluttering the cockpit. Over time one would develop the dexterity to scroll /zoom etc as it was an extension of their fingers. I completely disagree with you.
On another note I completely agree with an above post that a docking system that would charge the unit is is a necessity.
As far as phase of flight allowance your company makes that decision with the approval of your CAA. Usually an experimental aircraft for a few weeks with a fed on board to observe that the unit does not pose a threat to safety. Performed some test's of a component that emitted a cellular signal, we sat in the cockpit and went over all aircraft systems to prove there was no interference, it was about 3 days work.