The text was written without realising that you never have a negative modifier to your caster level
If your caster level was 0, which all non-casters are, the spell would fizzle.
this question has come up plenty of times before. Likely someone can link you to a Dev comment or previous discussion.
If you know the answer, just post it.
- regular piercing metamagic rod
- regular extend metamagic rod
- lesser empower metamagic rod
None of those buff CL. If that's what you want, this is the tool you need. Some magic spells can only be buffed by a CL increase. But all magic spells will be, and without taking up higher slots as with metamagic.