This shoe fit me wonderfully (I sized up a half-size as I often do for Merrells, probably about 50% of the time, shoe depending), was MUCH lighter than the regular All Out Blaze even with the waterproofing, and it breathes wonderfully. My reservations were with exactly what makes it that way - the patterns of breathable mesh. I was very suspect of how it would wear, both the upper and lower, and those suspicions seems to be confirmed by some reviews. I wound up returning these but I think they'd be a great choice for those that want a shoe for hotter days and don't expect it to last hundreds of miles. The pattern of the leather upper will, I think, allow it to wear better than many others but don't expect a miracle. The new All Out Blaze 2 and the new MQM shoes would be good choices as well, the latter of which is the lighter/airier, the former should last the longest.
Merrell makes a lot of really good shoes.