Well, I recently started to use the buckler. It's good and all.
But the main problem is, it blocks one hit (sometimes but mostly break when receiving it) on elite difficulty in tier 3.
So, I got a small suggestion...make a 4* and 5* upgrade for it. Just to block more and have more shield health. But for being such an useful shield, in offensive terms, maybe being the weakest shield of all the shield in 5*, being weaker than Barbarous thron shield, and with it, we can atleast block 1 attack succesfully (of course not a hit from Vana).
So yeah, that's my suggestion
Swiftstrike is meant to have weak defense. Combo it with Chaos for intense power.
You trade out one of your best ways of resisting attacks with a very noticeable bonus to attack speed. That's the way of the glass cannon. (That's not my style and will never be btw)