I've always found shoulder rigs more attractive in theory than in practice. (That doesn't mean I wouldn't buy the rig pictured; I own more than one for single knives.) The problem with shoulder harnesses for blades is the same as for handguns; they're awfully difficult to keep completely concealed and require a great deal of fabric over your torso to do just that. Of course, if the straps don't stand out against the shirt beneath, it's not as big of a problem, and I've had the straps of an Uncle Mike's ballistic nylon shoulder holster mistaken for suspenders before. But I tend to avoid shoulder harness carry unless it's cold enough to wear a bulky jacket (which is just what Jerry Van Cook is wearing in the photos in TK).
Cheap and expedient shoulder harness tip for large knives: Any knife with a tie-down strap can be carried under your arm by looping the tie-down over your shoulder. You can attack the knife to your belt to keep it firmly in place, if you wish to carry it that low. Add a little paracord to anchor it to your other arm, and you're in business. It's not particularly comfortable for any length of time, but it works; I tried it after someone on another forum suggested it.