I'm not a QFI although I do other training tasks within flying and engineering. More to the point I've probably flown with at least 20 instructors at various times.
Different students need different teaching methods. Different instructors apply different teaching methods - most instructors have a variety of teaching methods but not necessarily a wide enough variety to match all students.
If the other QFI is dreadful you'd know (and so would the CFI) from the stream of complaints. Presumably this isn't the case, so probably there's just a mismatch.
Tell the student this is probably the case, and talk to him / CFI / other QFI whoever is most appropriate on that basis. Make it clear you'd also send the other instructor a student you're not making progress with if you thought it'd help.
I got binned from the RAF at 19 because the (incredibly experienced and well respected) QFI I was flying with scared the S&*& out of me. I now am a reasonably competent pilot with about 400 hours, thanks to other equally competent (civil) instructors used different teaching styles. Had I understood all of this at 19, I might have spoken to the squadron CFI and still be flying the Queen's aeroplanes. On the other hand, I probably wouldn't be a Chartered Engineer - swings and roundabouts!
G