Use something else, of course the quality is fine because it uses LAME like almost every MP3 encoder out there, although it is 3.99.5 and not 3.100 for some reason. But the the files are missing information, I tried a FLAC file and it couldn't even retain the complete meta data of the FLAC file and the cover art was resized. (could be a limitation of the demo though) But that the MP3 doesn't even include the encoder settings and the default VBR setting not --vbr-new (fast) is a also not a good sign.
My suggestion is to use XLD, which is free and works much, much better and has much better control over the quality and handling of the files you want to convert.