CM108 USB vs I2S DACS - RPi

This a serious question… has anyone done any decent comparisons between the really cheap CM108 based USB soundcards and the range of I2S DACs available for the Raspberry Pi?

I imagine the I2S based DACs are better, but how much better to the casual listener?

I got a CM108 USB soundcard for 99p and I’m really impressed with the quality for something so ridiculously cheap.