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.
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.
Two more lines worth it.