require returns true on success,

yes, and false (undef) otherwise. That was the idea :)

string-eval eats memory

Why would that be (in this case, where the string is just a few bytes)?  Any tests/data to prove the claim?

C:\>perl -e"print require CGI;"
1
C:\>perl -e"print require CGIshamalamadingdong;"
Can't locate CGIshamalamadingdong.pm in @INC
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Not sure what this is meant to demonstrate — I thought we were talking about eval "require ...":

$ perl -E '$ok = eval "require CGI" ? 1:0; say $ok'
1
$ perl -E '$ok = eval "require CGIshamalamadingdong" ? 1:0; say $ok'
0
[download]

(note: swap single and double quotes if you're on Windows)