Michael - It doesn't sound like you've ever even seen one of these Durst carriers, or else you sure as heck don't know how to use one. You bring into focus an actual film crosshair target factory-mounted toward the front of the carrier. There are two different registered positions where the carrier locks into the head. Halfway-in, the crosshair lies directly over the center position of the baseboard (everything is fine-tunable). Pushed all the way in, your own film image (up to 5X7 format) is centered over the baseboard on axis. Therefore if you just focus on the film crosshair (much like a reticle), you attain the same focus usable for your sheet of film sandwiched in the carrier. Film plane A (crosshair) and Film B (you negative) are exactly the same distance from the easel, centered on exactly the same spot. In both instances, you are focusing on the respective EMULSION GRAIN ITSELF. Get it?
Junk?... Damn expensive "junk". Yes, they made even more expensive carriers; I have some of them, as well as their 8x10 enlarger equivalents. No one can afford that kind of true machinist quality production or die-casting for an enlarger model anymore. Every recent enlarger model is aluminum extrusion, CNC shaping, plastic parts etc. But you must think a Ferrari is junk too. Unless they're old and all beat up, or you are exceptionally lucky (it happens), these particular carriers by themselves often cost more on the used market than nearly all complete production 4X5 enlargers from other manufacturers, even brand new.
What kind of enlarger do you use? - a VW van with one of the headlamps inverted through the top as the enlarging light source, and the amount of pressure in the rear tire constituting the focus mechanism? Something you learned from the hippies who fled to Canada in the 70's? Either way, keep it - tie-dyed enlarger curtains will soon be back in fashion.