Its both

Then if you are offering it as advice to me, I reserve the right to reject it. And explain why. Which I did.

even all the units, of which he says there are 2526;

I made it 2571. It took me exactly 6 minutes to locate the source; download the file; unzip it; locate definitions.units; load it into my editor; and run 5 regex substitutions and half-a-dozen manual fixups to isolate that list. Which I then pasted into the data section of a script:

#! perl -slw
use strict;
use Time::HiRes qw[ time ];

my $start = time;
my %units = map{ chomp; $_ , 1 } <DATA>;
print time-$start;
__DATA__
...
[download]

And it took a whole 7 milliseconds to load the hash:

C:\test>junk3
0.00783705711364746
[download]

Its much better to badmouth them without investigation of any kind

1. I didn't bad mouth; just said that they were unnecessary.
2. I did investigated String::ShellQuote.

   Enough to discover that as only supports BourneShell quoting, it would be useless to me or anyone who needs to support some other shell. Which would then require yet another module and trusting yet another author.

   And for long enough to know that it would take me days to convince myself that the author knew what he was doing; and much longer to convince myself he'd covered everything.

As for IPC::System::Simple. I've investigated that before. And whilst I have seen modules that purport to be 'better' substitutes for built-ins that were more bloated, and/or more pointless, but there aren't many.

Now that is bad mouthing if you wish to see it that way.