Recent purchase: Rossi AI $299 from Golf Galaxy (this is the most I would pay for a putter) - 1 degree flat
Here's what I can pass on to others as advice:
I bought this club to help me get the ball to the hole (distance/length judgement) but
realize it's the small details that really matter with a putter.
I prefer a sight line perpendicular to target the line to help me square the face - this putter doesn't have one
Grip size makes a big difference - e.g. the difference between Flatso 2.0 and 3.0 is noticeable
Make sure the putter satisfies your preferences!