i use wensel woodsman heads pretty much exclusively, and with good results. there are two ways that i know of to sharpen them well enough to shave hairs easily.
the first method gets the blades straight - most are slightly concave, which will prevent flat file sharpening. i do this on a bench sander or belt sander with 120 grit - put the head on a shaft and lay down so the sanding belt runs from the back of the head to its point. do this quickly, about 2 seconds per side, don't get the head too hot and ruin the temper. then i put it on a 12" grobet file and push from back to front on each side 'til a burr is raised. i also "pyramid" the needle point, to make it stronger. i knock down the burr with very light strokes of a very fine diamond file or arkansas stone, then a final polish with light swirls on stiff cardboard.
the second method is to use a 6" grobet file, stroking each pair of blades from back to front - this follows any blade curvature. raise the burr on all edges, "pyramid" the tip, knock down the burr with very light strokes from a very fine diamond file or a stone.
there is another method i've only heard/read about, where you first put the edges on a 6" grinding wheel, light stroking across the wheel's stone - this creates a hollow ground edge that has less angle than if flat ground, that's sharper but a tad more fragile 'cause it's thinner at the edge.
hope this helps.