As far as I know, free spins have validity of 48 hrs only. So you need to use that before it expires. Otherwise, I don't think it will still be good for you to stack up those free spins.

But their decision for dplay casino to accept only FUN token would be beneficial for this token as it will encourage adoption for this token. Since FUN token is also available in a lot of exchanges now - https://www.coingecko.com/en/coins/fun-token#markets, it is not hard for the player to acquire this, not only from freebitco site.