As much as a longsword proponent as I am, Buckler is not only a blocking weapon, ohhh no.
It's a striking weapon with two modes of attack.
First is the broad mode, wherein the whole surface of the buckler is shoved against you, like a shield would be shoved. This virtually guarantees contact with your body, and can be used to stun or push away someone. Having had it happen, it hurts, can potentially break bone, and is not something done 'defensively.'
The other is the narrow mode in which the buckler is turned edgewise to impact you with the rim of the shield. This -will- break bone if done with a martial degree of force. Imagine an object moving as fast as a punch, then concentrating the force of that punch onto an edge narrower than your finger, and hitting you along the eyes or the ridge of your nose.
The buckler is a weapon, in every since of the word.
Do right, there is nothing else.