If I read well, the programmer is quite scared of someone breaking the interface - otherwise I don't understand why using this double-interface MyTemp/_Knob. I'd probably trust the user a little bit more and stick to _Knob directly, but that's a matter of taste.
Given the fact that it deals with temporary directories, I'd go a little further and encapsulate directory creation inside as well. In this way, you would reduce the risk that you create a temporary directory but forget to mark it as mortal (if you pass me the XS language). This makes me wonder if there's a CPAN module that already does this - if not, it's a good idea IMHO.
Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))')
Don't fool yourself.