The BTZS incident system is very easy to use. It is based on the fact that from the blackest black to the whitest white that can be created with paint is approx. 41/2 to five stops difference in reflectivity when evenly lit. Film speeds are tested as outlined in the BTZS system. A shadow reading in the most important area is taken at 2 times the tested speed. The dfference in stops between highlite and shadow areas determines the developing time. Specular reflections are ignored since it is assumed that they should print white. The system assume that all tones from white to black are present in both highlighted and shadow areas. If they are not present then you can either accept that fact or change exposure/development time to compensate. It is an easily applied system that does not require a great deal of practice. To make the system work properly, one must preform some sensimetric tests...readings with a desitometer are required. Charting is also required but they can be hand drafted. One must consult the BTSZ manual since the subject can not be fully covered here.
I think the pros and cons, at least for me, is that on does not specifically know which zone a part of the subject will end up on with the incident system thereby making visulization more difficult. Problems that a spotmeter can cause...such as sensitivity differences by color, flare problems and judgement regarding readingsof distant items, IR light sensitivity etc ...are eliminated. In the best world one would use both systems. The testing is the same and the charting requirements similar.