Not exactly the same thing. @ISA = qw/Exporter/; doesn't perform a 'require Exporter;'.

From the base POD: use base; "is rougly similar to":

BEGIN {
    require Foo;
    require Bar;
    push @ISA, qw(Foo Bar);
}
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I like use base; also because it runs under strictures without explicitly calling "use vars qw/@ISA/;", or declaring "our @ISA...". ...just a minor improvement, IMHO, but I prefer to use it.