Comparing BRUSH ONLY (32, 36 & 40 teeth) blades VERSUS (80, 100 & 120 teeth) MULTI-USE blades:
(A) if you run your trimmer at ultra high RPM’s then the larger teeth cavities of Brush Only blades will not be utilized properly as the material being cut is cut before sinking into teeth cavities. So some altering of speed with your Trimmer’s speed trigger may add efficacy when using less teeth but with larger teeth cavity style blades. Multi-use blades have so many teeth that you may find that although such a blade works with brush, it can tend to push over brush a tad more than a Brush Only style blade.
(B) Larger teeth Brush Only blades will have more friction when cutting limbs and branches, therefore will tend to seize (get stuck) more often in the cutting material, therefore you may wish to use a Multi-use blade with more teeth for such applications. Likewise, when hedging, thin rubbery hedge limbs can bend and tear when using a Brush Only blade as the deep teeth cavities don’t have carbide in them (only steel), so perhaps a Multi-use style blade is a better choice.