It's a really good idea to get the seat fitted professionally the first time, or at least checked by a professional fitter after you've done it. Until you are familiar with how to do it, it can be tricky, and it's easy to not do it tight enough. But once you know how to do it, it's fine to do it yourself, and you'll find you get quite quick at doing it. We have changed seats around from car to car often and not had a problem.

ETA We have found the ones that are just forward facing are easier to install than the reversible ones. But the reversible ones are really handy early, especially as rear-facing is a lot safer and most of those seats allow rear-facing until 12 kgs.