I use both Sta-flo starch and Best Press but for different reasons.
Starch will give a firmer body to the fabric and I use that when doing pieces that have a bias edge and Seminole patchwork. I mix my own at 50/50 starch and water and put it in a spray bottle. I spray the fabric and then roll it up and let it mellow in a plastic bag for a while so the starch is absorbed into the fibers. This is important and I try to not be too impatient about it. I have a plastic dishpan that I spray into to contain some of the over spray. When I press I have a piece of muslin over my ironing board to save my pretty cover. If some gets on my iron (not usually the case with this method) then I clean the sole plate of my iron with Magic Erasure (cold iron, wet erasure).
I use Best Press when I want some extra body and crispness to a block when I'm pressing the block. It gives a lighter touch to the fabric than starch.
I found the best spray bottles are the ones used by hair dressers as they give a fine mist. I got mine at Sally's Beauty Supply. They are not very expensive. If you don't have a Sally's in your area ask your hairdresser where she gets her supplies.