It means we haven't finished and polished the application the way we wanted yet. We don't have all the features we would like to see available yet. But we wanted to give you a taste of what we're developing and listen to any feedback you might have!
No. If you create decks on SpellStack we will keep them safe as we deploy new versions! After all we're users of this site as well and we don't want to loose track of our decks. If you're still worried, you can always use export feature to store your decks as text on your local computer.
Using SpellStack is free of charge