We made one this fall.  It sure looked like a good idea, but I can not say ours did any good. 

We made ours with 4 "fingers" per row.  We spaced them 10 inches apart so the standing corn would not be hit or effected so much.  One finger to help the corn in every 90 degrees of turn. The 10 inch's apart was O.K., but 4 fingers is to many.  It is like a fork in spaghetti.  Once it starts to wrap one stalk it will bring in others to be wrapped also. With all this rain, I am taking mine off and changing it to 2 fingers per row.  One finger to "help" every 180 degree of turn.  We used 1 inch tubing or the same as 3/4 inch pipe.  Instead of leaving the tubing straight at the end we used a conduit bender I had and put a bend in the end.  We put the bend in so that it is sideways.  I am also going to change that so the bend is the same direction as the corn coming into the head.  Maybe it will catch less stalks and have less wrapping.

I have seen some with a rubber hyd. hose clamped on the end.  I think the hose was something like  40 or 50 cents per inch.  To much money.  We did one row.  No help. 

If my corn was 100 % flat, it might be a good idea.

We had corn over 75% and it actually picked best when I picked the same direction the corn was leaning.  The ears were still tight on the stalk and had very little lose.  I could pick regular speed in this directions.  Now going against the leaning stalks it was 2 mph instead of 3 mph.  The stalk would break off and the whole plant went into the machine much more of the time. 

We it was only a $400 experiment that did not work and my time.  It was better than paying $2-3,000 and not having do what I expected. 

Enjoy.