One of the biggest cons is that above the tv is way too high for most people's optimal/comfortable viewing. There are several different opinions about the best height at which to view a tv, but generally when sitting you should be staring at the center of the screen or at the very highest at the bottom of the tv. Unless you have an unusually low-profile fireplace, watch tv standing or are like 6' 6" tall, a tv mounted above the fireplace is going to make for some uncomfortable viewing.

Could you post a picture?

Depends on how you want to style it, but I think this would look lovely and make your room feel nice and cozy.

I have a Jotul F500 fireplace which on the inside right wall is cracked. Can this be fixed please?