Listening to Solfeggio Frequency tuned music will have no major downsides, as casually listening is always a great way to achieve calmness. The only way you would be doing yourself harm is by listening to these frequencies at too high of a volume.
Never exceed listening to straight frequency tones over 60db, as volumes that exceed this threshold could lead to damaged hearing and tinnitus. Listening to a tone for a prolonged amount of time has shown to lead to tinnitus as well. When listening to straight tones of Solfeggio Frequencies, use these as a tool in active meditation.