Being able to map function to buttons is really useful but I just read that it doesn't have buttons on top. That is maybe a handling problem for me (although I do not know how serious) because mapping does not solve everything if many buttons are missing. Let's hope handling will be better than R. For example I miss the drive speed button which on R I can do it only via the multifunction button (and after some key presses with touch of course). Another issue is the lack of setting a whole set of functions to a button (just like EOS 5DIV, 5DsR, 7DII). I use this to switch INSTANTLY to another group of settings when there is a bird in the sky and I want to take a picture of it. Imaging using lower speed (to keep iso low) and 1 point AF when shooting something on the ground and you see a bird. You can switch to a higher speed, many point AF, possibly exposure compensation, specific AF tracking parameters, etc, all with the pressing of one button. Yes, one of 3 Custom mode settings could also be a solution but the button is even faster. And there is not even such a dial on EOS R5!