As you state, the only file size method in Net::FTP (the size function) tells you the file size on the remote system. File sizes can be different on different platforms.

My only idea of how to get an accurate file size locally would be to stat the file once it's been transferred. Something like:

my $file_size = (stat($filename))[7];
[download]

should give you what you want to know, if in a round-about sort of way. If you have more than one file, just use your favorite loop. As with all things Perl, TIMTOWTDI, and I am sure there are some guru's around with more clever ways.