No signal/ground noise that is noticeable by ear, even when using sensitive IEMs.
Plenty of more power compared to the stock amp/DAC in the phone, around 1.5x more (Galaxy S10 5G)
Sadly, not enough power to drive higher impedance headphones. 50 ohms might be maximum depending on the user's preference.
Soundstage/separation/imaging becomes slightly more clear compared to the stock amp/DAC in the phone.
A slight increase in detail as well. No discernable distortion until the volume is cranked up to max.
Overall, for phone use with IEMs, I recommend this product. However, if you have higher impedance headphones such as the Sennheiser HD650, I recommend looking at another product.