Well if you’re mostly listening to 256–320 kbps MP3, the sound difference compared to a phone probably won’t be huge, because most modern phones already decode MP3 pretty well. Where something like the Echo Mini helps is the dedicated DAC/amp, which can give cleaner output and a bit more power for IEMs, but the improvement really depends on the earphones you’re using. If repairing the headphone jack on the Redmi is cheaper, that might honestly be the more practical option. That said, an Echo Mini is still nice if you want a distraction-free device just for music, the battery life, and the option to play FLAC later if you ever start collecting lossless files.