IMO, the 3135 is a rip-off intended to suck more money needlessly out of noobs. It is NOT a clone in any sense of the Rolex movement, it is simply a clone movement decorated and modified to somewhat look like the Rolex movement to people who have no idea what they are looking at.
And since Rolex doesn't make a display back, the only people who will see your fancy-smancy 3135 movement are people who will remove the case back. And anyone with the wherewithall to remove your caseback will know what they are doing and will not be fooled for more than 3.8 seconds.
Now, as for the ETA 28XX movements vs. clones: a real, new, Swiss-made ETA 28XX movement is better and more desirable. This is NOT what you will get in most reps. If you pay for a Swiss ETA movement, you may get a new Chinese-made ETA movement (at best), or a factory second, or an old re-used movement, or on built up from new and old parts. The clone 28XX movements are arguably as good as the ETA movements you will receive in most reps, in both quality, reliability, and accuracy. The clones accept gen parts and even most experts have a difficult time telling them apart.
Also, you cannot compare the 28XX movements, or even 3135 movement, to a 21J movement. While there are some high-beat 21J movements available, usually when we talk about 21J movements here we are referring to low-beat $15 movements which, while they can be very dependable, do not compare in smoothness to the high-beat movements.
Hope this helped.