This summer I am renting a car with SIXT model size FWAR in Munich and I had a couple of questions regarding cars in that category.

My friend has warned me that most of the time the cars in this category have small engines such as a 3 banger in a full size wagon (I knew they had small engine but that's small)
I was planing to drive up mountains roads and I don't want to get stuck with a car that's full of passengers and suitcases.
Anyone rented this category lately and what kind of experience did you have?
I tried to look around the forum and couldn't find any information.

Thanks