I have a 20 year old site that I want to upgrade to a responsive layout. Originally it was a desktop-only layout but when a significant portion of my user base went mobile I implemented dynamic serving layouts where I sniff the user agent and serve different HTML based on whether the user agent is for a mobile device or not.
My current plan is to still do server side tests based on the user agent like this pseudo code:
use responsive-layout if (bot) use desktop-layout if (msie or firefox < 54 or chrome < 58 or edge < 16) use mobile-layout if (opera-mini or android-browser or samsung-internet < 5 or safari-mobile < 10.3) use responsive-layout otherwise
Most of my users and search engine crawlers would get the responsive layout. Only specific non-capable and older browsers would get my existing static layouts.
I know that Google supports either responsive layouts or dynamic serving layouts but I haven’t been able to find any information about a hybrid approach like this. Are there any pitfalls (especially with regards to SEO) of mostly using responsive but falling back to dynamic serving for some browsers?