OP you aren't being anal, just sensible. I think it is possible to get a bit too anal about car seats. And I say this as a person who reads far too much about them in general as I find them weirdly fascinating!
IMO, buy the safest you can reasonably afford for your own car and regular journeys. Rearface for as long as is practical. Don't push over into what you can't afford, that's not necessary - there are cheap enough seats on the market these days, though I would stick to trusted brands (Generally the cheap ones which are alright are either Joie or Britax.) I don't like Nania or their clones. (These tend to have rucksack style strap adjustment, not the one-pull method from the bottom of the seat - easiest way to spot.) The line which is currently going around about keeping children harnessed until they are about 9 is misleading - it's OK to switch to a high backed booster when your child outgrows their seat as long as the booster fits them well and they can be trusted not to wriggle out of it. In fact some believe this is safer than a forward facing harnessed seat because the play in the seatbelt puts less strain on the neck than a fixed harness. (Loose harnesses are dangerous, so you can't counter it that way). It is worth using a booster seat until the seatbelt stops irritating your child's neck without it and they can bend their knees over the edge of the seat with their bum against the backrest, even if they're over 135cm at this point. There's no actual max weight for boosters (either type). A properly fitting seat is safer than an outgrown one but in general the lower the age group, the higher the protection offered.
It's okay to relax the standards for occasional use or tricky situations.
The Freakonomics data is sound actually, and does apply to European seats too and has been repeated with modern seats so isn't outdated. However it only looks at figures of death, not serious injury - so for age 3 to 135cm in height, I would still say that seatbelt only is for really unavoidable situations. It's better to have them on even a cushion booster (better a highback booster) if at all possible. Luckily these types of seats are easily portable and extremely cheap. IMO if you have a child over 3 or 4 you should always have at least one spare cushion type booster, for transporting extra children or for unexpected/tricky trips for your own child.
Any car seat is better than none. This idea that anything less than the shiniest, newest thing installed perfectly is a death trap is incorrect. It's true you should pay close attention to fitting advice because sometimes incorrect fitting can cause dangerous situations, but there are reports from the 70s and 80s of seats which have been installed totally incorrectly, with children of completely the wrong age group in them, seats which would never pass any safety testing today, and yet they have saved children's lives.
Never share a seatbelt between two people, especially tucking a baby into an adult's one. Don't use cushions or other items as makeshift boosters - without the reinforced hooks to hold the belt in place it's more dangerous than using nothing. Don't tuck the shoulder belt behind a child or under their arm. And be extremely cautious about front seat airbags and children as these can seriously injure them.
I will never forget reading a post on a parenting forum when DS was little from a poster whose mother worked as a police officer in a country where the car seat laws were lax, meaning she saw accidents with any combination of unrestrained, poorly restrained and properly restrained children, in good seats, bad seats, forward facing, rear facing, old, new. She said that the children who were restrained survived car accidents, and the children who were unrestrained did not. It did not matter what type of restraint was used.