I'm not very keen on the Emerald, it's one of those seats which combine all the stages into one, and as a result you get compromises in all of the stages.
If you are really really keen on this concept, Avionaut Stardust is a better option because the rear facing mode lasts longer. It's not a huge amount more expensive, and it's cheaper than the Axkid One3. I feel like this would tick a lot of boxes for you from what you've said so far - worth a look?
Chat GPT is possibly out of date on the Besafe izi Modular X1 being the highest rated RF/FF model according to currently comparable ADAC tests. It is on the top of one of the tables I have (which has REALLY confused me, because this is based on a fairly spurious calculation I did - so I'm intrigued as to how ChatGPT came to this conclusion) but that's only current up to Spring 2023. At a very quick glance, I believe Joie i-Spin 360 and Cybex Sirona T outperform it, however I do need to go through and update everything with the more recent test results.
Bear in mind this is a bit of an inexact thing and ADAC don't test every single model on the market, so I wouldn't put too much store on it definitely being the safest seat anyway. ADAC can give you a rough idea of how a seat performs compared to other similar ones, but it's hard to compare across categories and you don't really want to be using it as an absolute measure.
The izi Modular is also not a spin seat, it's a slightly older model, (it was tested in 2020) and it's one where you use the base you've had from a baby seat, so you'd have to buy the base assuming you don't already have a Besafe izi Modular base. You can install the seat in either direction, but you don't get the spin function. It's a good, well made and well rated seat, but it's not the best thing you can buy for the money IMO.
There is a version of this (Modular A X1) which has an auto-tightening harness, which is a really nice feature, especially if you're likely to use the seat forward facing in the future, but it's fairly niche and not necessary if you tighten the harness properly yourself.
Besafe have a spin model which doesn't need a separate base, called Besafe izi Turn. That is my favourite out of the spin seats up to 105cm, but it is usually too expensive for people to choose it compared with other models. It's especially good for cars with sloping back seats and low-down isofix points, because it uses its own method of levelling to achieve the correct angle independent of the vehicle seat. However any belt fitted seat e.g. Axkid Minikid, and Axkid One also achieve this (in their own ways).
Then there is also Besafe Beyond which is a spin seat (plus separate base) which goes up to the 125cm. Price for seat + base is similar to the Axkid One3.
Or as different direction - you could look at a cheaper spin seat to 105cm with a good safety rating, like Cybex Sirona Gi i-size, or Britax Dualfix Plus, or Maxi Cosi Mica Eco, or even a Plus tested spin seat up to 105cm (Joie Spin Safe, Britax Swingfix Plus, Axkid Spinkid, Besafe izi Twist) and when your child gets close to 105cm, make the judgement whether you want to continue rear facing (in which case, a cheaper more basic but still plus tested model like Britax Safe Way M or Axkid Minikid 2 or Minikid Core), continue forward facing with a harness (several models available with harness over 105cm just recently; in three years there are likely to be more) or move into a high back booster.
On 50th centile, 105cm should get you to about age 4.5 - so any of the options would be a good choice, and if you decided to FF at say age 3 instead, you could look at seats with a FF harness which convert to high back booster, which is combining less stages into one.