My husband installed the seat and thought it was easy but we have a different britax already. I cant really help with the question. There is a youtube video you can watch for installation. This is the only car seat my kid has ever slept in so it must be comfortable.
It's easy. The way the seat it designed give me plenty of room to tighten the seat down without the seat belt latch getting in the way. (Which I have found to be annoying on other car seat that I have helped put in my car.) I do have a Tahoe which gives me space to maneuver and jam my knee into the seat to get it as tight as possible, so that may be an issue for you because you have a sedan. The base of the seat is long and takes up a lot of room, but it's workable for us. I love this car seat as does my almost 3 year old. He is always telling me he likes it. :)