Positive Putter's heal shafted model called the STROKE SHAVER is like the insert as the speed dose not vary on off center hits.
Striking the ball any where between the heal and toe weighting in the cavity portion of the blade will provide the same energy as a dead center hit, which is the perfect spot or sweet spot.
This will be true for any heal shafted putter that has been retrofited by Positive putter to Target-Line Balance or what some call reality balance.