The Iron Cutch is just that, a crutch. It was shaped like a large tonfa except that there was a bar at the top for leaning on. The exact configuration is questionable as each person made their own based upon body type. How many bars stuck out, what angle, and how/if any of the piesces were bent, all were subject to the whim of the user. The similarity was in the basic technique. The blocks, attacks and even some of the locks/throws were equivilent across china and japan. The only difference was that you can use to tonfa but you can't use two iron crutches. The large version is rare but any tonfa knowledge will convert pretty quickly if you find yourself hobbeling around for a week or two.
The energy benefit is that you would learn how to use any energies or skills while off balance and/or on one leg. The Iron Crutch would be a precurser to any begger forms, crippled forms, and/or drunken forms in your respective system. Most of the tonfa I have looked at tend to be used as a stick with a hook. I learned other ways.
In Iron Crutch, a lot of the techniques end up in some sort of grappling capacity with the opponent being choked, locked, trapped, and /or bruised in some way by the crutch. It tends to be underestimated because of the way it is used. The appearence of the techniques are clumsy and off center. This is because they are supposed to be. If you see a cripple using one to get around I would suggest you stay out of his way. If he knows how to fight with it you will have no chance, RUN.
This weapon tended to be used by styles that had levels or forms that could be titled "begger, crippled, and/or drunken". What the weapon helped with was the control of the center of gravity and balance. It was by divorcing those two concepts that allowed the unique forms of power generation that the three named styles/variations were capable of.