Hellobee Boards

I am by no means an expert since we only use ours when we rent cars, but we have the Boulevard and have been happy with it. My husband is the one who installs it and it seems to be pretty easy (we are traveling with it this week). It is flight approved and we have brought it on a few international flights and it fits in the seat (front facing, no idea if you could do a rear facing seat on a plane). My older LO can sleep in it without his head flopping, but we just switched our younger LO to that seat (and she is a peanut) and her head flops when she sleeps. As for rear facing in a small car...when we moved to France 2 years ago we were in a small car and couldn't RF and have the passenger be comfortable, so we FF when DS was 14 months. But "small" is relative when it comes to cars, we were using a Renault, which is probably smaller than a small car in the US market.

We have had a lot of Britax (replaced after several accidents ) and we have one Evenflo as a grandparent extra. So while I can't speak to the one that you are toying with, I can say that every model of Britax we have used has been so easy to install. In one accident our kids were in the car (it was the biggest one, with both vehicles written off) and the kids were both totally, 100% fine and barely shaken up.
We found that they do take up a lot of space while still rear facing, but that is almost unavoidable! And I found that (when rear facing, as things change when they are FF and more upright) were super comfy in it. It was like a huge lounge chair for a little body!
Good luck with your decision!

We have the boulevard and have no complaints. I can't answer most of your question because we use it in an SUV and don't move it. We just bought a second seat for our other car. My husband did say it was easy to install. My LO is 7 months old and sleeps fine in it. His head doesn't droop.

I have the Safety 1st, and I don't like it. It was very hard to install rear facing (I have not tried forward facing). I was also only barely able to get it sufficiently reclined for the over 22 pound level.

The front passenger seat has to be pushed up so far it is virtually unusable (Nissan Frontier).

I never tried to put it on a plane.

No issues with head positioning.

I think it will be adequate when I switch to forward facing. I would recommend the Britax Boulevard. I only got the Safety 1st because it is capable of rear facing for longer, and my LO tall. However, I think either way he would make it to 2 years.