I have not seen, in person, the D&D beyond application so all I have viewed is what has been release though media announcements and what I have read on their forums. What I have seen so far of D&D Beyond it will require a internet connection. Yes, it will have a Android and iOS apps, but those will still require a internet connection. There have been request for a off-line mode, but I don't think and Dev has answered that question. I could be wrong and they have announced a off-line mode for the apps, but I have not seen or heard that announcement. Also, the product is still in beta as of 8/2/17, so things are subject to change.
I would hold off making any decisions either way until both products have been released to the general public, in their final forms but, that is just me.
