Right, but if you take it, you then become a multiclassed Swordmage.
Multiclassing (by default) in 4e is done through feats. You take Multiclass Feats to become multiclassed. Essentially, this will let you take future feats to swap Warden powers out in exchange for Swordmage powers.
Now, I'm not a solid rulesninja enough to tell you if there's a Swordmage power that might be really worth that feat cost. If your Int is decent or your Strength is decent, Warden and Swordmage can play pretty well together, theoretically. You'll be a handy-dandy teleporting/area marking machine. You'll be mostly a warden, who can do some neat things with their sword when making melee attacks.
Which might be nice. Or at least fun for you.
It might not be
mechanically optimal. 4e characters aren't often disarmed for any reason. I guess maybe you could slap your bond on a dagger or something and throw it, retrieve it, and repeat. But that's not exceptionally effective.

If you were looking for raw power, I'd grab Weapon Expertise and Weapon Focus and Toughness and Sudden Roots (and that's basically your first 6 levels' worth of feats).
If you wanted to go with a optimized multiclass swordmage, I might recommend Blade Initiate instead. It will mean you don't need a shield as a warden, and, even if you use a shield, you'll get a +1 AC anyway, which is always cool.
If you were to go and take swordmage powers later, I'd steer towards powers without the "Implement" keyword, and without the "Aegis of *" lines. Those are the most likely to be useful for you. And, hey, there's some fairly neat abilities there, though likely nothing that's going to stand out as amazing for a warden to have.
But that feat, by itself, does make you a multiclass swordmage, and isn't, by itself, all that useful.