As great as this example is, I generally live in fear of browser-specific behavior.
In the best case, it solves the niggling inconvenience of having to click on the correct browser extension to install.
In the worst (and far more prevalent case), poorly coded browser-specific behavior stops me from accessing websites at all if my user-agent doesn't match something on the server's limited whitelist, or nags me continuously to download a "modern" browser while I am, in fact, running the latest build of Chrome or Firefox, simply due to a poorly configured regex.
The biggest useragent problem I have these days is clicking a link to a specific article on some site with my phone, and getting redirected to the front page of their totally separate mobile site, left with no way to find the article I was trying to read.
The second biggest problem is actually with software like Dropbox that's cross-platform, and the download page automatically chooses the version I want. Dropbox itself actually gets this right, by presenting small links to each specific platform right under the main download button, but I'm always running into sites that make it hard or impossible to get at a specific platform's version different from the one identified in my useragent string.
In the best case, it solves the niggling inconvenience of having to click on the correct browser extension to install.
In the worst (and far more prevalent case), poorly coded browser-specific behavior stops me from accessing websites at all if my user-agent doesn't match something on the server's limited whitelist, or nags me continuously to download a "modern" browser while I am, in fact, running the latest build of Chrome or Firefox, simply due to a poorly configured regex.