1. Technically there is no reason to avoid 528. It is not nickel. 528 is way to low to be anywhere near a resonant frequency of an elemental particle.
528 is just a frequency, and if it resonates with something in your system, it will do work.
As for the Solfeggio and being associated with Solfeggio.
Well that's an entirely different matter.
While we can draw connections to the 432 Hz scale and mathematics of the universe, there exists no tie in that I know of behind the Solfeggio. Just the info that the group that looked to re-discover it, puts out into the world.
Personally, I feel that the numbers used for the Solfeggio, are a method of classification for numbers. Based on the Rodin Family Number Group, describing the positive, negative, and magnetic emanations.
There's some stuff for one to go research.
Anyhow, if you were to run your phone number as a frequency, you don't expect it to call you now do you?
If you run a number that has a meaning behind it, I don't expect that meaning to carry over unless you put intent behind it.
Otherwise, it is just a frequency that has potential to resonate.
2. Here's something else to consider. The Solfeggio frequencies are 396, 417, 528, 639, 741, and 852. They look like perfectly good frequencies, no? Let's try pairing them. We get 396 and 639, 417 and 741, and 528 and 852. Now you can see the issue.
For more details, please check the link: