No, that is not necessary. As soon as he has scanned the VISYT code, he will be forwarded to the menu of your restaurant. This is the so-called web version. This is similar to the version that can be downloaded. With the web version, the guest can neither save photos of the dishes nor give a rating.
However, the download of the app is absolutely free of charge for everyone. The guest can also see which restaurants he has already visited and he can choose a restaurant without having the VISYT code. A selection is available both by the location and by the name of a restaurant.