Have a look here, where I have been playing with PWA (not yet finalised). The install button will only be shown in browsers that recognise installing a web app and hides once the app has been installed.
This excludes anything on iOS and Firefox 
Of special interest:
PS: Please excuse the quality of the images, this is a work in progress.
Off Topic: The business operates in a very competitive market and was just about to go bust, partly because of poor Google/Bing ranking. Within a period of a month, the rankings have changed. This can be illustrated by using a search term like Limo Hire Frankston or any of the other services in the footer. More will be added.
This is what the Admin section looks like:
Thanks goes out to my adopted son, Brian English (@Hyperbytes) for supplying videos that help to collect the thoughts for this old codger.