How durable is the iPhone X screen. Should I consider a screen protector and will they affect performance?

I cant speak to the screen durability, but I took my X to the Apple store as soon as I received it and had them put on one they sell (like I always do). They put it on with a machine and it is aligned perfectly. Very happy with it so far.

I will add while I‘ve never used a screen protector, I always have used a case (9 years with iPhones as my only telephone). My personal preference is for Sena leather folio cases (I like their look and quality). These do cover the screen when not in use so it’s never exposed to anything in my pocket or briefcase.

I have an Otterbox Defender with the screen protector punched out, and replaced with one that I had Apple install. It's a tight fit on the plastic part for the Otterbox, but will snap on. When I purchased my iPhone, I went balls out with protecting it.

If you are concerned at all get the screen protector. If you get one designed for use on the X then it will not affect performance. As for the type, google is your friend.

I have never owned an iPhone that wasn't in a good case, nor without a good quality screen protector. These phones are pretty expensive puppies, so some protection seems a very worthwhile expense.

Whether to use a screen protector or not with any iOS device is a purely personal choice. Some people use them, some don’t. Same thing with a case - some people use one, some don’t. Your choice.