I agree.. to give any feedback.. we need to know more about your project(s), and intended usage..
Do you have a preference between MP3's & WAV files?
I have played with the Waveshield and have experience with it.. but have never played with or used any sort of MP3 module/chip to decode .mp3 files..
I also suggest reading the comments about items from the users.. they usually post good & valid topics that pertain to the item
such as some modules can ONLY play files if they are numbers 1, 2, 3 ,4, 5..etc..etc.. some you can use/pass in a file name..
I found the stock/default Waveshield to be NOT very loud.. (although I read about adding a resistor for a volume hack that might help this)
Waveshield can only play 1 track at a time (can only open 1 file on SD card at a time).. not sure if others have same restrictions or not..
outline what you plan to do with it might help sway our suggestion one way or another.