You should do it. It was my first trail marathon too. Really is a fantastic course. You won't regret it. Take your time and enjoy it. As you'll be there for the weekend anyway, Would be a shame not to.
It's more the mental aspect of this event. You never get that far away from the start/finish. It's a procession of ups and downs along numerous finger like paths. So you go up the dreaded stepping stone stairs 4 times. You visit the halfway mark twice??? You visit the end once but that's only really the halfway point??? It'll all make sense when you doing it.
I guess with conventional out and backs or point to point races there is a sense of 'there's only one way to the finish line'. This one tests you much much more mentally. IMO.
It's tougher than those three. Mostly due to the nature of the course. It's like a hill rep session from hell. With great atmosphere, plenty stairs, great views, brilliant medal and shirt, friendly organisation/marshalls etc.