It should work either way.
Under the hood, the ‘Reapply while relevant’ option actually works by embedding a very similar relevance in the action, causing it to become non-relevant for the specified time period.
Using the custom relevance allows more granular control of the time period.
You can also specify both ‘Reapply while relevant waiting X time between reapplication’ along with ‘Reapply whenever it becomes relevant again’.
Using the relevance on the fixlet itself does help to guard against another operator running the action and failing to set the reapply delay.
So you have several options there from which you can choose what works best for your environment.