Actually the proper way to shift a non-synchronized transmission is to double clutch. Clutch the transmission out of gear, re-engage the clutch to allow the input shaft to slow down (or speed up in the case of downshifting) to the proper RPM to match the tail shaft, and the clutch the transmission together into the proper gear.
While you are correct that an un-synchronized transmission CAN be driven without using the clutch, that tears up transmissions even when there is no "grinding" indicative of "missed" gears. Ask an Eaton representative if he loves truck drivers who don't use the clutch. He'll tell you that's who pays his salary...
<----class A CDL licensed driver with a 1990 Kenworth T900, 13 speed Eaton roadranger, Detroit series 60.