Moved to Android.
Honestly, this is a question for AndroidCentral if anything. If you ask here, you'll get more responses about Android's inferiority than would probably be helpful.
In my opinion, it's a competent phone and it'll work but I would look into using a custom ROM for up-to-date software. (but I believe you'll want to avoid carrier-branded devices in that case, I may be wrong but I believe they've mandated locked bootloaders for a while now)
It'll be stuck on Marshmallow, which'll work fine on it's hardware (my daily driver's on Marshmallow too) although I don't know how much overhead Samsung's additions add and it's probably not getting security updates. (hence custom ROMs)
I have a friend who uses a 4 as their daily and it works for them. I think the biggest question is whether you're getting it for a good price.
It also has a removable battery which is helpful in case the current one is worn out, I think it's a sizable plus, especially since the phone was released in 2014.