We use windows based EFBs class 1 for the last, hmm, 10 or so years (no paper charts since). Since we do not have a fixed docking station we are not allowed to use it below 1000ft AGL, it has to be stowed below that altitude. A docking station would have to withstand the same accelerations as a crew seat in a newly certified airplane (26g crashload? don't remember exactly). Additionally if it is to remain in the docking station at all times it has to be readable in all lighting conditions, which is not all that easy to certify. Our military standard rugged pen tablets weigh around 5kg each and the display does not conform to the lighting standard, not to mention to certify a docking station for that weight.
We are now slowly switching to a class 2 device which is fixed to the airplane and has to be certified to the above standards and additionally that it does not interfere with the airplane avionic system since it is connected to it (one way connection avionics -> EFB).