I used it for a small while before I decided it wasn't for me. The effects I noticed were things like more quality gained on fire unstable successes, and less dura loss on a wind unstable failure. The elements that affect success don't really seem to be changed, because as OP mentioned I still got a lot of failed synths/chaotics (which oddly enough would be the reason I would use it if it worked).

The only decent technique I even try is to guess which element will go unstable (which is hard and often random) and use the specific ele resist skill, and wait it out.

Most of the time, I just hope it doesn't go unstable or at the very least chaotic, so I think there are better ways to spend the points.