The Challenger™ is an amazing overstable putter, and very popular with advanced players. It can get around trouble for those long hyzer putts and is overstable enough to take a good amount of snap on approaches.
"I carry four Challengers. One brand new D for putting and putting only. One is old and used for touch shots and long putts. Another D Challenger is somewhat used but is straight. I like the feel of the Challenger for putting, upshots, straight short drives."