Any version will work with F2P. But you might want to just install it online for free, save your money, and then decide if you want to subscribe to Champs or not once F2P comes out next week.
Actually, you needn't do that.
If you download the Demo fron Atari via the Champions site, it does not register as a demo, and if you log in to Champions via the link in the launcher once downloaded & installed it automatically grants you Demo access.
No cost, thought it will indirectly cost you bandwidth and time.