We used a capsule for DD1, rear seat for DD2 and capsule for DS. I think a capsule was great for a winter baby as we had him all rugged up in it to go out to the car not having to unwrap him to put him in a carseat. DD2 was December in Darwin so that didn't apply although we did find the car had to be cooled down before we put her in so if she had of had a capsule it would've been cooler I guess.
If you can borrow a capsule i say do that option but if you have to buy one and a car seat I wouldn't bother.