There is some explanation about usage of SSD and thumb drives in the FAQ section “What USB Thumb Drives work well?”. The info is available at https://cymaticaudio.com/support/faq
Regarding your last question, it has already been explained that the speeds of the same SSD vary’s depending on what is happening internally. You never know if starting from a freshly formatted SSD drive, the behavior will be exactly the same as before. That is why we do not recommend SSD drives. With improving technology in this field, it might mean that there shall be no dropouts with some of the SSD’s. But we cannot guarantee it.