bouncing down the track into mp3, itself, degrades quality. basically, to compress it to that size (not the same as zip compression, this one is irreversible) it removes unimportant frequencies, such as the highest, and lowest frequencies, as 20Hz is not really heard at all. its felt. and 20KHz is beyond many peoples audible range, as human hearing degrades below that as we grow. but yeah, if you work with audio, you will notice the difference in quality between the original work, and the mp3 bounce. The advantage of mp3 is.. the average listener will not hear the difference, and file sizes are much smaller. despite that.. now going to download the pack and have a listen.
EDIT: nice stuff! liked the vengeance drum sounds best though, and the Arp melodies.