It is a bit overwhelming Harri! I still want to stress that the safest car seat is the one that fits your child and your car the best. So if you can sit your DD in each seat you like with or without Securafit, and she fits better or is more comfortable in one without the Securafit and you trust she can sit still the whole trip and not move the belt then go with one of your first choices from CREP results. If you aren't confident about using only the adult belt I'd go the Securafit. Same as getting a good fit in your car, if the seat doesn't sit right maybe a different one is better.
So many variables!! Sorry hope I haven't just confused you more.

We had two nights of sleeping 10pm to 5am, yay! But missy has been asleep for nearly two hours now whereas she was awake playing the last two nights. I wonder what tonight will bring? I just long for consistency! *Sigh* Oh well could be worse, but the suspense is killing me