But if your putting is so bad that you feel that you need to "putt" with an iron your best course of action would be to take some lessons.
I decided to try using a mid iron not because my putting was bad, but because I suspect that using the iron for the longer distances will generally be more accurate than using a putter. When slightly off the green in the fringe, and even close on the fairway, using an iron gets the ball in the air for a bit and over the long grass. Its much better than a putter from those positions. So why draw a line when on the green at a distance. The only difference is that one is going over some long grass and one is not. In both cases, there are fewer divots, dings, spike marks, and other irregularities in the air to alter the ball's trajectory than there are on the ground. That may be ten to twenty feet or more of green I don't have to read and account for.