What do you do with it? It’s not going to be suitable for modern apps due to you being stuck on ancient firmware. Even Safari won’t support websites these days. I have seen people complaining about the iPad 2, which is the equivalent of a 5S, struggling to do basic web browsing.
You are right about Safari, it’s totally unusable - I’m using Chrome instead.
Majority of apps installed back in the days still work the same as day one. I’m using all the basics like Mail, GPS, camera, calendar/schedule apps etc.. I believe the case for longevity is dropping updates at some point (still running iOS 6).