Traffic subject to this feature cannot be handled fastpath and will be handled in at least the Medium Path. It does not appear to always force this traffic F2F/slowpath (which would not be good), but this DNS traffic could end up in the slowpath anyway if some other condition is present requiring it. Unlikely that enabling this feature would cause any noticeable performance impact in my opinion.
Attend my Gateway Performance Optimization R81.20 course
CET (Europe) Timezone Course Scheduled for July 1-2