As a microgrower, I found the mystery freebies to be frustrating. Not knowing if they were indica or sativa, fem or reg, photo or auto, 8 week flower or 14 week flower, made it too much of a gamble. With limited space and a restricted number of plants, I didn't want 'mystery'.
I don't want to waste them and I finally have a bit of a stash built up, so I've have started popping the occasional one. Now I'm finding the concept of mystery a little more appealing, especially after seeing the first girl I got. I'd still rather know what I was growing before I started though.