The SA3135 could be technically considered as „the first attend“ to reverse engineer / replicate the original 3135 Rolex movement.
When it comes up, it was kinda messy & several of them broke / fail shortly, regarding to where it was assembled and has issues with quality.
Since it exists since decades and over time the quality of the production enhanced a bit, so „newer ones“ could be considered more stable.
Unfortunately, the availability of parts for it, is still problematic & (more important) parts couldn’t be replaced with Genuine Rolex parts because of the design.
A while ago the SH3135 comes to market, which has a much more „genuine style“ technical design (but also has flaws).
The SH3135 is known as somehow more reliable, even while some of them also have technical issues, which might be because of the way they get assembled. (Consider it was build in someone’s dusty basement without using the right tools nor trained employees)
The best with this kinda movement is, that „most“ of the genuine parts could be used & fit into (except balance & anker).
However, the SH3135 was used (&still is) by several Rep fabrics until today and received some minor evolution.
Latest evolution of the SH is the „so called“ VR 3135 (which is the best out of stock you can get today, besides genuine, in my opinion)
Confusingly fabrics like NOOB seem to fall back to the older SA3135 (e.g. in their V10), which I’m not 100% sure if this is true and if yes, why..
An excellent comparison about the 3 movements could be found here:
https://forum.replica-watch.info/forum/the-3135-3131/7439844-3135-movement-comparison-gen-sa-sh-vr
