It's really rather simple: Incident metering measures the illumination itself, reflectance meters measure the actual amount of light being reflected by the subject. Both methods work well if one knows how to interpret and apply the readings.
However, often incident readings are taken for the primary illuminating source only (i.e. sunlight) and applied as though the contrast were "average." This results in underexposed shadows in contrasty situations. Taking the incident shadow reading and extrapolating exposure and development from that (often not so "quick and easy") by figuring lighting ratios, and how one wants black and white objects in both light and shadow to be rendered, eliminates this problem.
Reflected readings allow one to do roughly the same thing by taking readings from the actual values reflected from the subject. Still, one has to interpret and apply the data.
The accuracy and consistency of the exposure depend on the effective interpretation of the meter readings. Choose the complexity of your interpretive system (e.g. Zone System, BTZS, etc. or just "by guess and by golly") according to your needs and personality. Some are happy with a large amount of exposure variance, others not. There will always be some.
The only advantage I can see to reflective metering with a spot meter, is that one can get a rough idea of how differently colored areas of the scene will be rendered on the final print (e.g., if adjacent red and green areas will "merge" in tonality in the print) by checking their comparative reflectances. This is, unfortunately, limited by the mismatch in spectral response of the meter and film, so that only a general idea can be had from the readings. Experience with one particular combination of meter and film can allow better interpretations of the readings, however.
My personal preference is for the 1° spot meter, since I can evaluate specific areas of the scene as described above, and see how they relate to each other. This helps with visualizing the final print. Also, I prefer to meter through filters, for the same reason. I have to apply a lot of "fudge factors" and compensations when doing this, but I find it superior to simply applying the manufacturers' filter factors.
Spot meter readings have little advantage if one feels no need to compare specific areas in the scene.
Best,
Doremus Scudder
www.DoremusScudder.com