Are dual-function AFCI/GFCI breakers less effective than single-purpose GFCI breakers?
They should be equally effective. They have a job (or two jobs) to do, and are designed and tested to do that job.
But I would suspect a higher incidence of False Positives nuisance trips*, particularly since you can't have one part without the other. One option to consider is AFCI via breakers and GFCI via receptacles (first in each chain), which also provides easier reset. AFCI is, generally speaking, protection against either internal wiring problems - e.g., nail through a wire or worn out (or rodent chewed through) insulation - or certain significant failures (backstabs or other bad connections, worn-out electric blankets).
On the other hand, while GFCI does provide protection that can substitute for the &quot;usual&quot; ground wire (since any current that would be going over ground must be &quot;missing&quot; from hot/neutral and therefore an imbalance == GFCI trip), it also provides protection against true device ground-faults and certain temporary problems, particularly due to water getting inside electrical equipment. As a result, having easy and convenient reset for GFCI is potentially more useful than for AFCI. In addition, while AFCI is important for the wires, GFCI is for receptacle/device/people protection, so putting it at point-of-use (first receptacle in the chain) works very well.
*I initially wrote &quot;false positives&quot;, thinking like incorrect spam filtering or rapid COVID-19 tests. However, in the case of GFCI trips, the vast majority of trips will be true positives. The issue is that many (not all) of these so-called nuisance trips will be situations that can be resolved easily &amp; safely. Spill water on your toaster (or other appliance with internal exposed wiring) and you will have temporary ground-fault that will be resolved by drying out the appliance. But that trip is still real and potentially deadly, just temporary. Unlike, for example, worn out insulation where the danger never goes away (and the GFCI trips keep happening).