is this absurd or logic way to erase Flash memory?
Then, I am not speaking of legally compromising anyone. I was asking, first, if a sd card, or an mp3 player, or a pendrive could be totally erased, so anyone could get back anything.
With flash memory, you are stepping into probabilistic forensics. There is no definite, 100% answer to your question. The answer to your original question would be "yes, that technique works good enough" in a sense that the end user will not be able to recover anything from the device after the wipe procedure you described. There is also a very good probability that even a forensic expert will not be able to recover anything, or at least nothing meaningful. And there is a 0,0…01% chance that some chunks of data may be recovered from the flash chips after the wipe due to redundand storage capacity and the way wear leveling operates.
You can read http//articles.forensicfocus.com/2012/10/23/why-ssd-drives-destroy-court-evidence-and-what-can-be-done-about-it/ to get an idea on what happens with information stored on certain types of solid-state memory (that includes higher-capacity pen drives and certain high-capacity players but not yet SD cards, as far as I know).
How much are you willing to take this device apart, and then put it back?
How much is the device worth on the street?