MacUpdate Desktop saves you time by fully installing and cleaning up Mac apps with just 1-click. But not all apps are compatible with the MacUpdate Desktop engine (around 91% work properly).
When you click to Install or Update an app within MacUpdate Desktop, if the app is compatible with the 1-click engine, it will do everything for you and you'll see the "Open" button at the end.
However, if the app is not compatible with 1-click, it will still download the file just like you would have done in your web browser. Once the download is complete, you'll see the "Show File" icon. Click it and manually install the app.
Essentially, MacUpdate Desktop saves you a lot of time. If the app ends up being compatible with 1-click installs, it will install. If not, then it will display the "Show File" button where you can manually install it once it's downloaded. This allows you to have a more uniform experience where all of your downloads and installs can occur within MacUpdate Desktop.