What you have looks reasonable to me.

From a module-consumer perspective, I sometimes use Exporter's regex feature to get all the exports from a module that neglects to set up an :all tag, e.g. use Foo "/./";. This tripped me up once with a general debugging script that did -MScalar::Util=/./ when isvstring was added. It got trapped by export_fail prior to 5.8.0 and just croaked :(

$ perl5.6.2 -MScalar::Util=/./ -we0
Vstrings are not implemented in the version of perl at -e line 0
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