More than one way to skin a cat, as the saying goes.
I agree that the best way to manually focus is to use magnified LV. This usually means the camera is best placed on a tripod, but can be done hand held with the method of moving yourself back and forward to achieve perfect focus. I don't use the AF aids in LV. When magnified 100% my eyes can do a quicker job just as accurately.
However using the OVF is also a valid method, but you need to practice your skill or you will get missed focus. Photographers (myself included) used OVF for decades, with and without focus screen aids.
I do also use the PDAF AF indicator (green hexagon) when manually focussing with the viewfinder. But if you use this method you need to make sure your cameras AF Fine adjustment is calibrated correctly (if needed) in the global (APPLY ALL) setting. Otherwise you will get missed focus.
I took this shot handheld with the K1 and M* 300mm. I relied solely on AF confirmation in the OVF. .............