One of my clients does not have a QR code reader on their cell phone. How do they access the menu?
The client can go to mobilemenu.es and access your menu from the list of centres or download and install the QR reader direct from Google Playstore.
From personal experience, I find one of the easiest to use is the Kaspersky QR reader and scanner, It's free and NO ADS.
You can download and install it here https://play.google.com/store/apps/details?id=com.kaspersky.qrscanner&hl=en_GB
How easy is it to change or insert a new dish. For example, if the chef adds a new dish of the day?
It's really simple. You have direct access and control of your own menu and can change ingredients, description or prices of any item and even add new ones at the click of a button.