Many calls we field at Sensenich come from owners who have changed the original design of our propellers, sometimes through overpitching, or blade cutbacks, and simply stamped them as EXPERIMENTAL. It's always upsetting to us, as this can cause extreme safety issues.
All of our propeller designs have been thoroughly tested by our engineering department to ensure that they are safe for use. At times, this might involve placing an rpm restriction for some models, or a "no diameter redution" on others...for example.
There is a very infomative document in our documents section with some important definitions regarding this topic.