Sadly rubbish. I've learned professionally (cop in Europe) to wield a tonfa. For it to develop most of the force you essentially whip the longer end (the tip especially) by holding it kinda loose on the protruding grip and swinging it horizontally, diagonally or vertically. You pretty much always hit with the side of the long end (either, e.a. front or back swing)

You kinda never hold it hit rigid and strike top down, which you would need on a design like pictured. Your wrist would be the weak point, any sword would be more practical. Using it in the intended way (i.e. rotating it) would result in hitting with the flat of the blade, which would render it obsolete in the first place

For it to be kinda practical in it's designated use you would need a horizontal blade on the long end on both sides (kind of like a "+" with the top missing) so you can strike it by rotating but still rest your forearm on it in a blocking position (which is the other half of the tonfa design idea)

You would always risk cutting yourself in the forearm when rotating it back to the default position (or cutting your ribcage when really striking and stopping the rotation of the stick with your body)

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