Thanks for the input.
I am afraid you use of the phrase "Pure Perl" is confusing me. Normally I would take this to mean a module that is implemented purely in Perl (without any calls to C etc), but that is not the way you are using it (since at least the CPAN implementations of Blowfish and Rijndael I am using have binary elements).
I guess when you say "Pure Perl" you are focusing on the fact that these can be obtained from CPAN (and / or ActiveState) rather than the other challange of implementing modules on OSs that provide an inadequate set of tools for developers (where if perl is available but there is no good freely available C compiler a Pure Perl module will always work).