Floodgate is a good investment, yes. Useful in any deck. The other good cards are : Horus (anti-spell deck), Magical Something (may be interesting in a Monstermorh deck / Magic Counter deck), King of the Swamp (good in every fusion deck), Card Guard (control deck), a lot of good Ninja support cards... It's one of my favorite box.
PS : It depends if you're only a "I want to be KOG" player... I love building good deck, even if they are not viable in Legend to reach KOG. This game is much more fun when you can switch between different decks.
I was thinking about building an horus deck... but with six sams, GB, CA I don't think it is worth it anymore, am I wrong? And yes, I don't want to be only a KOG player, I also like building and testing other non-tier decks, but when you are going to spend 10000 gems on a box as a f2p I expect more than a simple test-deck...
im a casual player play ranked sometime mostly for fun for me this box is pretty worth it if you want to try some deck like horus , king of the swamp, ananta reptile , card guard, magical someting, de-fusion bunch of good sr too
if you have a competative deck and it still working fine just stay with it dont open every single box if you f2p you just gonna waste your gem dont get baited by all the youtube deck i mean if you want to try it its fine your owm gem not mine i manage to save my gem by skipping a bunch of box