Based on extensive (if anecdotal) experience, undergrads really cannot cope with more than a single reference, which must be traversed in order, possibly omitting some sections. Having any other source is somehow beyond imagination. Subject=course=textbook.
Grad students can do somewhat better, but are not happy about having to operate at a higher level. Perhaps understandably. Obviously habits from undergrad have inertia.
The most bizarre negative side effect of not "just following a standard textbook" is the occasional suspicion from the students that the instructor doesn't know what they're doing (no matter that they might be a respected expert among their peers, etc). I recall being taken off guard when an undergrad couldn't believe that, in fact, I was the author of the text being used for the course. The idea of author as authority looms very, very large in peoples' minds. (Some etymological connection there, too.)
That is, at lower levels, using several sources (in a math class as opposed to literature, etc) seems to so violate expectations that the instructor's credibility is lost in the minds of a substantial fraction of the student population. Somewhat less so with grad students, but still non-trivial non-sequitur problems. E.g., especially before I had the advantage of a gray beard and bald head, divergence from the students' preferred reference was viewed as lack of preparation, or negligence, on my part, even if/when I explained to them that we can do better than the usual sources.
At the graduate level, especially beyond first-year things, I've tried to change the perspective... by writing my own notes (yes, a bit of work), with historical references, explaining chronology, and so on, the idea being to get students thinking in terms of the subject rather than secondary or tertiary sources.
Unclear to me how successful this is, but I feel professionally obligated to give a push in the right direction.