No issues, not one. I wouldn't call it flawless since the menu system is overkill (Canon rules in that dept) and it's a bit too easy to accidentally hit buttons (so I map them accordingly) Maybe they just didn't like the ergonomics, we are all built differently. Mine's with me until it dies. Great tool.
What do you mean by open it?
Usually after downloading the update, one puts the sd card in a card reader attached to the computer and uses the Finder to drag the update file over to the sd card’s icon and drop the fie on the icon. This copies the file to the outermost level for the card. Then eject the card, put it back in the camera and start the camera part of the update process.
Here is a feature that caused me some grief. If you select Auto for Dynamic Range, the LCD and EVF will no longer display shutter speed and aperture except when the shutter button is pressed halfway. It took me a while to figure out why shutter speed and aperture were missing from the display.