I've never seen perlite that had a consistent size. If you want consistent particle size, you've gotta screen it yourself.
There's no way baling pressure causes the perlite in promix to crumble.
Why do you care anyway? Consistent particle size is what matters if you want lots of void space.
Otherwise, the smallest particles will fill all of the cavities. In this case, peat would be the filler.
Perlite is added to reduce the amount of water a given volume of soil can hold -- not aerate it.
I'm really not concerned with how consistent the size is. I'd think that a little variation would actually help. As far as the perlite being crushed into dust from bailing I've seen it myself. Open up a bail and more often than not everything that looks like a piece of perlite is already a pile of dust. I don't think that particles that small are going to do much for improving soil texture. Even the manager and other employees of the store I go to agreed about not using bailed soil for the same reason.
Perlite is meant to improve texture. It will hold more water than some types of soil after being watered but will also hold pockets of air after the soil has had a chance to dry out bit. Look at almost any soil mix made for high drainage/aeration and they will, more often than not, have a higher ratio of perlite.
It's beneficial for improving soil in either direction except for the fact that it doesn't keep its consistency for very long. It's no big deal if you're not reusing your soil or using it in long term planting beds but I'd at least make sure that the perlite hasn't been crushed into dust before you even buy it.