I thought independent calculations were the industry norm, especially after the emirates overrun with their airbus in melbourne.
In my opinion the iPad software is much better than the windows software we used before. Some options are rather well hidden, but still, the inputs and presentation is much better to work with.
In my outfit it was always two independent calculations. One with the preliminary figures (either preliminary acars loadsheet or OFP figures), which is necessary to get the engine out procedure and then program it into the secondary and subsequently brief it, and then a final one with the final acars loadsheet. The second one is of course easy to do, simply modify the take off weight, press calculate and wait a bit. That procedure hasn't changed really in the change from windows to ipad.