I find the efficient version much clearer, too. It extracts one layer of abstraction: a beginner may wondering, how can a variable being less than a function (a<func()), then find out, that the function returns a value, etc.

Two more lines worth it.

I've been back and forth about how to respond to your comment. My initial reaction was "'func()' is a call and therefore returns an expression." Having thought about it, I don't really remember what my neophyte reaction would have been.

It shouldn't confuse students with optimization advice, but with the authority the lecture holds on malleable students, your asterisk should still be mentioned as an FYI for good measure.