Nope, it works very well. I have been testing it routinely for a decade now. The core to it is simply getting the "mobile" keyword out of the user agent string

Nope, it works very well. I have been testing it routinely for a decade now. The core to it is simply getting the "mobile" keyword out of the user agent string. That takes care of nearly everything, from there all you have to do is a simple css split for either desktop or mobile. It very effectively covers all the major browsers, all the major platforms, going back at least a decade.