The Surly Corner Bar is certainly a great way to add a drop bar to a flat bar bike without the expense of changing your group set.
A really nice design, that is comfortable, well made, super durable and looks cool in that funky Surly way.
It's heavy, but doesn't seem that noticeable when fitted to your bike (unless you ride a super light weight bike). The only negative for me is that it's a bit expensive (Aus $).
Overall a great product for it's intended use with multiple comfortable hand positions.