modified ETA is what that means. Some prefer non in house movements, I have both, and they keep great time either way. good luck and congrats on the new watchI can relate with OP. I'm also having some difficulty finding sources with details on their in-house movement. There are also some controversies going around saying Breitling is only retuning existing ETAs.
I just acquired a Superocean 44 on the used market. It looks good, but I have difficulty finding info on it's movement, applied tech etc. I do know it's using B17 in-house movement though, whatever that means.