I ignored all advice to the contrary and purchased a park tools lockring wrench. I needed one immediately, and it was all the LBS in town carried. This was the worst 16 dollars I have spent in a long time. The thing was barely willing to grab the lockring. The tooth on the end seems like it is actually curved in some way. I am also fairly certain that the metal is so soft that I thought I was going to break it.
Whatever you do, don't buy this wrench.