I have been using the Sta-flo and not having a problem with it lasting or going bad. I guess I use it too fast but I make it up by the spray bottle , one from the garden center. I do use distilled water don't know if that makes a difference. I added rose water to mine and it was really nice to smell that when I ironed.
I found something awhile back but no one carries it anymore. Dryel made a starch alternative and I loved that. They stopped making it however I can't even find it online anymore.