Bio Spira has ammonia and nitrite bacteria in it, not just one.
true, but in a tank without nitrite (like a new uncycled one) the nitrite eating ones quite possibly will die before the amnonia eating ones make enough to sustain them, thus the double dose thing. ;-)
Second dose on the nitrite spike.. may not always be the case, but it's kinda better to have a little left just in case, imho.