It seems that people don't quite like others using Swiftstrike Buckler. I was even kicked out of a group for just using one!
I can hold my own fine in Tier 3 with Swiftstrike, and although it's not the greatest shield, the speed bonus helps.
So, why does everybody hate the shield so much?
I've never played with a good player that used one; usually the ones that use them in T3 are speed freaks with ego problems that like to just charge into things and not pay attention, and play exclusively in groups for free revives.
Unless you're that good(which very few people are), the additional health on your shield is much more important than the speed.