I'm wondering if anybody has extra info about the above seats I've not found yet. Expecting DC2 in August, don't have DS1's old car seats any more (he's 140cm and just on a low booster). I had narrowed it down to the Cybex Aton or Aton 5 as a newborn seat, but DH wants to look at 0-4 seats as well now. We have a Suzuki Swift which is quite small but has isofix, top tether, no underfloor storage.
So :) Here I am in the happy land of research 
We live in Germany, so availability is different to the UK. We also have access to France. Price is, unfortunately, a squeeze point.
I'm aware of the benefits of a Group 0+ seat over a fixed one in terms of portability and convenience, so that will factor in but I'm just looking for info on some of these seats, if anyone knows. It also may be that getting a 0-4 seat now might be our best shot at affording to RF beyond the infant seat at all.
I'll list what I've found so far and if you can add any additional info, I'd be really grateful. We'd be looking to use the seat from newborn. I don't know whether we'd do RF right to the limits of the seat or not - discussion/decision to make later. I'm aware it's 5x safer. For me the important thing is to RF over a year - to 18 months/2ish as a minimum. We're not likely to have a tall child.
Joie Steadi
- Non isofix
- RF to 18kg or FF from 9kg
Safety: Struggling to find info - Joie seats seem to vary. I am concerned about side impact scores despite ERF fans insisting RF frontal impact being the only one which matters. I'd like to have as much info as possible about scores in any direction if I can.
Pros: Harness is easy to adjust. Flexibility in longer RF if desired.
Cons: Seatbelt seems to be in the way when placing child in seat, only RF position is reclined (is this correct?)
Chicco Cosmos (I know this isn't a UK seat so it's a long shot! But it's the only 0-4 seat I can find under €100 - trying to see if it's a false economy.)
- Non isofix
- RF to 13kg or FF from 9-18kg
Safety: Difficult to find. Chicco seem to be raved about in the US for their safety but only get mediocre scores with ADAC for their other seats in Europe. One batch of this seat had a recall because of a potential issue which makes me think the company do care about safety - not waiting for a third party to discover a fault. But I'm not sure how I feel about the brand in general.
Pros: Comes with a newborn insert?
Cons: ??? - RF to 13kg only which could be limiting. Couldn't find other info.
Concord Ultimax 3
- With isofix
- RF to 105cm, FF from 15 months
Safety: The Ultimax 2 seems to get a Good ADAC rating but the 3 hasn't been tested. Other Concord seats get Good/Very Good results for safety. It looks like it failed the Swedish Plus test in FF mode but that's to be expected from any FF seat. I wasn't clear whether it just got a mediocre RF result or whether it wasn't tested, because the site wasn't easy to understand with google translate.
Pros: (Based on Ultimax 1/2) - Seems to fit very well and sturdily in the car without moving. Flexibility in RF for longer. i-Size so I don't need to argue over RF until at least 15 months 
Cons: (Based on Ultimax 1/2) - Difficult to adjust straps when child grows, some reviews mentioned parts breaking and Concord being unhelpful about it - unsure whether this has improved? It seems like a big downside.
Other seats I've seen which look good (but could find more info about easily!)
Hauck Varioguard Plus
Joie Spin 360
Seats I'll consider due to budget but am not hugely keen on:
Britax First Class Plus - Currently to me this seems similar to the Cosmos, but the Cosmos is cheaper here (FCP is €150+)
Joie Stages - Really only worth it because of the lack of need to buy a HBB later, but I may rule this out yet.
The three I've detailed are the ones I'm not sure yet if they're in the "look good" category or the "acceptable if budget is really tight" category.
TIA! :)