I think this solution would work best for squarish packs than those that are round.  I've used this technique several times when packing luggage (a squarish container), but my gear pack is more rounded.  I still use stuff sacks for that pack.  I've found if you don't "stuff" the stuff sack that it will conform nicely into an irregular shape, thus filling what would normally be a void.

As for the square (air bleed) zip locks.  They are heavier than even the heavy duty zip locks and the nylon is a bit slicker.  The downsize for travel is that when placed on a flat surface (like a bed) they tend to slide all over the place rather remaining stacked.  After a while, I was afraid that a bag might slide off the flat surface into a cranny and be left behind.  So, I've mostly ditched using them for luggage-based travel.

dd