I use both spray and sta-flo. I will say that the sta-flo allows me to make the fabric more stiff (I just add less water)....I love this for my backings--seems to help keep everything in it's place and I tend to have less puckers.
However, since it does seem to go bad quite quickly (not sure if it's b/c I'm in Arizona), I only make a small amount when I mix. Maybe putting it in the fridge might work, but it only takes a minute to mix.