There's a lot to say about this split. First, it features one great name (Mouthbreather) and one lesser one (Environmental Youth Crunch). What strikes me second is the contrast in band styles, though I'll elaborate on this later. And, third, that it's such a solid release with five songs - it's an EP, not a single.
First on the record is Mouthbreather. They play melodic hardcore that walks the line between street punk and thrash. John Martin has a big lung, posturing feel to his screams and the songs flow well, building energy and then dropping the tempo back down every so often for the pit stompers to catch their breath. The thrash influence lies underneath the more structural elements to their songs. Good stuff, meant to be played loud.
As for Environmental Youth Crunch, they play poppier music that is a strange pairing with the heavier Mouthbreather. EYC play something similar to your run of the mill Plan-It-X bands. It's pop punk with jagged guitars, sloppy vocals, and incredible brevity. They pack three songs on their side with plenty of room to spare. I'm intrigued, but I'd like to see them work the melodies into something a little longer, since the 0:28 "Leap Year" stands out as their best song. The 1:50 "Slow Jamb" is, indeed, their longest song and it actually feels long in comparison with the other songs.
As a nice change, the lyrics are printed on the inside of the cardboard sleeve instead of as an insert.